To reduce the size of a current limiting resistor connected to the contact of a circuit breaker, switch, etc., by on/off controlling a switching means and, while the switching means is turned on, detecting the state of the contact of a serial circuit to which the switch means is installed.

Remote monitor and control equipment is provided with a switch section 1 and prevents a current I from flowing except during a data read section 3 performs data reading even when a contact 120 is turned on by controlling the switch section 1, so that the section 1 may be turned off when the data read section 3 does not perform data reading by means of a data read timing control section 2. The switch section 1 is constituted of a photodiode 1a and a phototransistor 1b. The photodiode 1a is controlled to emit light by means of a control section 1. The phototransistor 1b is provided between, for example, the contact 120 and an insulating circuit 111. In addition, the components of the switch section 1 are not limited to the photodiode 1a and phototransistor 1b.