I had entered in Thailand with passport after that I get a new passport from my Embassy with the Letter from Embassy.

So, when I was entered in Thailand, I was anticipated to write anything into the Departure Card,, and then the case of number of passport into of Departure Card I write the number passport who now was already cancelled and replaced by new passport.

Then, when I'll exit Thailand, I need to erase the mistake old number of passport write into my Departure Card, and replace it by the new number of my new passport or not ?

For information I use "O" single visa, without extension, and will not do extension also.

I suspect immigration will take care of this on departure - believe they will also mark your new passport. You just present both passports on exit.

I had exactly this situation recently. It's the new passport number you should enter. But anyway Lopburi is right, immi will take care of it.

I hadn't altered the number when I handed my new passport over (with the old dep card) & the officer pointed it out, crossed out the old number & wrote the new one.