To properly keep the temperature, humidity, and dust concentration in a control panel using simple means, even when the control panel is installed at a place in an inappropriate environment outside an air-conditioned room.

The insides of the control panels 30A, 30B, 30C installed outside air-conditioned rooms 10, 12, 14 are ventilated by introducing air from the air-conditioned room 12 ( or air conditioned rooms 10, 14) into the control panels 30A, 30B, 30C. In this case, ventilating air is introduced by ventilating fans 32A, 32B, 32C disposed on the control panels 30A, 30B, 30C.