PURPOSE: To prevent mutual interference between an ISO information detecting means and emitting light quantity changing means, by providing an impeding means which at least works during the operation of the ISO information detecting means and impedes the transmission of the output of the means to the emitting light quantity changing means.

CONSTITUTION: When a switch 62 is closed during a charging period, the output S62 of an inversion circuit 63 is inverted to a high level and transistors 71 and 50 are turned on and, as a result,a supply voltage Vcc is generated. Therefore, a transistor 85 is also turned on and the operation of an oscillating booster circuit 12 is stopped. The charging operation to main capacitors 16 and 17 also stopped. Moreover, when the switch 62 is closed, the output of a NAND gate 6 is inverted to a high level and a transistor 68 is turned off. Therefore, flowing out of an electric current through a resistance 70 does not take place and an operational amplifier 36 normally operates as the current adder circuit of electric currents flowing through resistances 39 and 40. From the output of the current adder circuit, an analog voltage indicating ISO information corresponding to an electric intercept existing on a film patrone 41.