Doesn't really look like Box Blight - the cobwebby stuff indicates some sort of pest rather than an infection, and the new growth looks normal. Not sure what the pest might be though, where you are.

Ok, thank you, Bamboo.
I had seen there several very thin and lightgreen caterpillars, but I didn t know, if it is related to those "spider-like webs".

Box tree caterpillar probably - don't know how long its been in your country, only just arrived in the UK. Sprays containing pyrethrum have some effect, but picking the caterpillars off is possible.The RHS has a page on this, so google Box tree caterpillar

THANK YOU, Bamboo.

The Buxus died last week.

Shame - what treatment did you use?

I picked caterpillars, which were visible, and then sprayed it with some chemical, which was recommended to me in the shop. I think that wasn´t the only case and Buxus had both diseases.