To provide a controller which can reduce the power consumption at waiting for operation.

In a hot water supplied where the main body 1 of itself and a remote controller 2 are connected with each other through two communication lines 23, the remote controller 2 is supplied with a first voltage through the above communication line 23, and also the data of operation information, etc., are modulated into high frequency signals and they are superposed on the above first voltage, whereby communication is performed between the above hot water supplier main body 1 and the above remote controller 2, and when operation of the above hot water supplier main body 1 is interrupted or at the main body 1 is at waiting for operation for more than a specified time, only the switch operation detecting circuit 15 of the above remote controller 2 is supplied with a second voltage smaller than the above first voltage, and also the above superposition of the high frequency signal to the second voltage is stopped.