The present invention provides an expansion appliance which can be inserted without cutting new incision during surgery requiring the endoscope medical device and with no need of extra personnel to be able to continuously ensure the maneuvering area or the eyesight around the treatment portion. The expansion appliance system (1) is installed on the treatment tool (12) used for observation through endoscope (11) and guided to the front portion of the outer tube (14) inside the body cavity. The expansion appliance system (1) comprises: the airbag body (61) which can be expanded or contracted and is expanded toward the direction away from the aforementioned guiding tube； and the exhausting tube (62) which supplies fluid to the airbag body (61).
