A source voltage monitor for a photographic camera is adapted to determine, prior to release, whether the source voltage is at a level sufficiently high for effective release for exposure. The monitor uses a predetermined reference voltage for the comparison, which voltage is selected independently of the selected mode of photographing. According to the invention, the source voltage is checked prior to release with a lens barrel driving circuit and/or a shutter blade driving circuit energized, depending on the selected mode of photographing. In the preflash mode, for example, both the lens barrel driving circuit and the shutter blade driving circuit are energized during the source voltage check. In low luminance automatic strobe discharge mode, only the lens barrel driving circuit is energized during the source voltage check.