PURPOSE: To keep the internal temperature of a camera rear part, namely the film, at fixed temperature showing an optimum value by controlling an electronic circuit by an electric resistance so that heat is generated at the internal part of the camera rear part and providing a heat sensor near the self- developing film.

CONSTITUTION: The electric resistance A connected to the electronic circuit F is disposed in contact with a wall E, and is made active and stimulated according to a signal from the heat sensor D. All the parts are hermetically sealed and protected by a backing B made of heat insulating material. Meanwhile, actuation circumstances, that is, whether the internal temperature is proper for exposing or developing the film is known from the external part through a warning lamp G. A large space is formed at the internal part of the camera rear part separately from an existing space as a place to house the resistance A, the sensor D and the film, and also the electronic circuit F is inserted in this space. Thus, the internal temperature of the camera rear part, that is, the film is kept at the fixed temperature showing the optimum value.