Don't try to do this validation with a Validator.
Cross field validations can't really be done with Validators (not without JSF 2.0 or a lot of painful code. Search this forum for it)
Just write the validation as part of the application invoke stage in your save action or whatever button they push.
Alternatively, perform an ajax call with each check of the checkbox that toggles the required attribute of the textArea and rerenders it.
Thanks, yes, i figured it out that cant use standart validators...
But could you give me example of code? Tried few variants already, but get stucked, that checkbox value doesnt updates
Rather than me doing the work for you, how bout you post what you've tried and then we can discuss why it doesn't work.