To provide a monitoring camera lens device where a diaphragm is manually adjusted by remote operation, if diaphragm adjustment by automaticx adjustment (automatic iris) is not suitable, by executing the changeover of the automatic adjustment (automatic iris) and the manual adjustment of the diaphragm.

An iris controlling motor 38 is automatically driven by an automatic iris circuit 40 so as to set the brightness of a video signal to be proper by inputting the video signal from a camera 12 to the automatic iris circuit 40 in the case of executing the automatic adjustment of the diaphragm by the automatic iris at a lens device. When an iris selection signal to instruct the manual adjustment of the diaphragm is inputted from a controller 16, the connection of the iris controlling motor 38 is switched from the automatic iris circuit 40 to the side of the controller 16 by switching the switches S1 and S2 of a switch circuit 44. Thus, the diaphragm adjustment is executed by the controller 16.