PURPOSE: To facilitate up/down control of a zoom lens by selecting any of at least three resistors connected in series between a point of a power supply voltage and a point of a ground potential.

CONSTITUTION: Operation switches 20a, 20b to set a zoom lens 1 to have a prescribed magnification are provided in a zoom camera unit 4. The operation switches 20a, 20b are connected to both ends of resistance division of a power supply wire from a control unit 18 and its midpoint connects to an A/D converter circuit 15 of a section 9 of a control unit 18. The zoom camera unit 4 electrically connects to the control unit 18 by a cable. When the operation switch 20a is depressed, a resistor 20d is short-circuited and the mode is set to the zoom-up mode and the magnification of the zoom lens 1 is increased. When the operation switch 20b is depressed, a resistor 20e is short-circuited and the mode is set to the zoom-down mode and the magnification of the zoom lens 1 is decreased.