A proximity sensor (1) includes a state updating section (22) and a control section (5). The state updating section (22) updates state information. In a case where the state information is updated with a state (ST1) or a state (ST4), the control section (5) supplies, to the outside of the proximity sensor (1), a signal (S6) indicating that at an object (B) to be detected does not come close to the proximity sensor (1). In a case where the state information is updated with a state (ST2) or a state (ST3), the control section (5) supplies, to the outside of the proximity sensor (1), a signal (S6) indicating that the object (B) to be detected comes close to the proximity sensor (1).