A switch state detection circuit according to the present invention comprises: a plurality of switch connection portions to each of which a switch is connected, a connection line to which any one of the switch connection portions is connected in a switchable manner, a detection portion that detects a state of the switch connected to the connection line based on a state of the connection line, and a connection control portion that switches successively each of the switch connection portions and connects it to the connection line, wherein the state of each switch is detected.