Firstly thank you for your quickly answer.
We use firebird version 2.1.
You can see tables row counts in following list.

STOKDEPO 2 rows
SHRKTNM 10 rows.
STOKKART 1000 rows.
SHRKSTR 1000 rows.
SHRKBSLK 500 rows.

We believe that the query (including all sub queries) does not process/products results around 1.000.000.

Firebird is slowly when running subqueries, does it may be.
If it is true, what can we do about it?
Thank you.