To realize a good print processing of various types of matter being printed including envelopes by eliminating generation of creases or lowering of print quality at the time of printing on an envelope.

The print mechanism 1 employing a thermal transfer system for printing on a matter P being printed while clipping at a print section 5 having a platen roller 2 arranged on one side, and an ink ribbon 3 and a print head 4 arranged on the other side is provided with a platen change mechanism section 6 comprising a plurality of platen rollers 2a and 2b having different physical properties which can be used selectively depending on the type of the matter P being printed including envelopes.