An electro-developing type camera uses an electro-developing recording medium including an electrostatic information recording medium and an electric charge keeping medium. The camera has a transparency sensor for detecting dark-zone-transparency data at a portion of the electric charge keeping medium corresponding to a dark zone defined on a light receiving surface of the electrostatic information recording medium. It is determined whether or not the dark-zone-transparency data is substantially equal to reference-transparency data. If the dark-zone-transparency data is not substantially equal to the reference-transparency data, it is warned that the electro-developing recording medium has been recorded on.