PURPOSE: To prevent the seizure of a color filter and the occurrence of a photographing-unable state by setting a specified small diaphragm state with an independent control means in a lens unit when an appropriate diaphragm control signal is not transmitted from a main body unit to the lens unit.

CONSTITUTION: Incident light on an ordinary photographing lens 1 is outputted as an NTSC signal from a camera encoder 5 through an image pickup element 3 and a camera signal processing circuit 4, etc., and a brightness signal outputted from the circuit 4 is supplied to a camera microcomputer 10 through an integration circuit 6, etc., then the appropriate diaphragm signal compared with a reference value from a reference value setting device 8 is supplied to a lens microcomputer 17 in the lens unit LU through a data transmission line 18. In the case that abnormality occurs in the transmission line 18, the diaphragm control means in the unit LU does not follow the output of the microcomputer 10 but fetches the stop value detected by an encoder 11 in the microcomputer 17, and compares it with an initial stop value previously set and controls a diaphragm 2 to prevent excessive input.