Those are not the clearest pictures, however it appears that budgie has a VERY bad case of mites.
Treatment needs to be ivermectin or Scatt Spot-on Treatment.
Do NOT use mite spray or home remedies.

This case looks as if it is advanced and the budgie needs to be treated right away.
Do you have an Avian Vet?

Additionally, when you bring home a budgie, it should ALWAYS be quarantined.

Quarantine means housing the new bird in a different cage in a different room than the current bird (as far away from the room the current bird is in as possible) for a period of 35-45 days.

Budgies mask symptoms when they are ill. Symptoms may not show up for over two weeks.
Often you will not even realize your bird is not well. Many budgie illnesses are airborne which is why you need to quarantine your new bird in a completely different room.

Quarantine - Is it Really that Important?
Quarantine Your Birds

How many other budgies do you have?
How large is the cage in which you are housing them?
Where did you get this latest bird?

 

Seller told me that it is female. I thought female budgies have some stronge marks on beak. She's one year old if he didn't lied. I will try to make better pictures tomorrow in daylight. If we judge from photos mites then I will go to avian vet. I already treatet one budgie from mites before. It looks like it is common diease in my area.

 

I would agree that it is a female, they do not have marks on their beaks any differently than a male, however, when a female budgie is in breeding condition the cere my turn a dark crusty brown. It does not look anything like what you see on the bird in your posted picture.

 

Yes, the budgie is FEMALE and she has scaly mites. She needs to be treated as I previously indicated.

Do you have additional budgies at this time?

 

I have additional budgies in second room.
Here's better picture with flashlight

100% mites?

 

Yes, she has a VERY bad case of mites.

I recommend you remove the plastic dowel perch and replace it with
Natural woodperches of varying diameters to help prevent pressure sores.
Pressure Sores
Bumblefoot
The information in this link will give examples of better options for perches:
Essentials for a Great Cage

 

Terrible that whoever sold you this bird let the bird suffer with this for so long, this did not happen overnight, please seek out vet treatment asap.

 

Sorry to see this precious girl suffering like this, glad you're able to get her the care she needs since clearly the seller was not going to.

 

One more question. How long it take to see first visible signs of mites from infection? Month?

 

Generally, as soon as mites start burrowing in a budgie's legs/feet or beak you will see signs within a few days.
In your budgie's case those mites have been there much longer than a month.
The first signs of mites generally start off at the edge cere right against the beak.
Whomever you got this bird from has known the budgie was infected for quite some time IF that person pays attention to his/her birds at all.

Have you taken the bird to an Avian Vet for treatment yet?