To reduce electric power consumption without worsening ease-of-use of a system.

In a system 100 connected, via a communication line 41, with a plurality of devices 10, 20, 30 having respectively communication circuits 11, 21, 31, electric circuits 12, 22, 32 and electric power sources 13, 23, 33, the devices 10, 20 are constituted to take power saving stand-by conditions where only the communication circuits 11, 21 are brought into operated conditions, and standard operation conditions where the electric circuits 12, 22 other than the communication circuits 11, 21 are also brought into operated conditions, and electric power consumption controlling means 14, 24 are provided to control the power saving stand-by conditions and the standard operation conditions in the devices 10, 20 to be switched by a command transmitted via the communication line 41.