To prevent the damage of an ultrasonic element even in a case that a tissue treatment device is erroneously operated artificially or mechanically in a state that a liquid such as a chemical liquid or the like is not present in a tissue treatment part in a tissue treatment device using an ultrasonic wave.

The tissue treatment part 1 for treating biotissue has a double structure and an internal liquid 2 is injected in the internal layer of the tissue treatment part 1. A plurality of ultrasonic elements 3 are arranged to the lower part of the tissue treatment part 1 and a injection and drain port 4 for injecting and draining the internal liquid 2 injected in the internal layer of the tissue treatment part 1 is provided.