A multiple optical axis photoelectric sensor in which a plurality of optical axes are provided between a projector and an optical receiver, the multiple optical axis photoelectric sensor being configured to repeatedly perform: optical axis scan processing, in which the optical axes are activated sequentially to detect the presence or absence of light entrance for the activated optical axes, and determination processing of determining whether a detection area formed by the optical axes is in a light entrance state or in a light obstruction state, based on a result of the optical axis scan processing, and to switch on or off an output in accordance with a result of the determination (ST9, ST11, ST16), the multiple optical axis photoelectric sensor comprising: malfunction notification means for notifying that an output indicating the determination result that the detection area is in the light entrance state or in the light obstruction state is due to a malfunction; characterized in that the multiple optical axis photoelectric sensor further comprises: variable update means for updating a first variable and a second variable according to the determination result of the optical axis scan processing (ST23, ST24, ST26, ST 27), the first variable indicating a duration of the optical axis scan processing for which the determination result that the detection area is in a first state is obtained, the first state being one of the light entrance state and the light obstruction state, the value of the first variable being updated as long as the determination continues that the detection area is in the first state (ST24, ST27), and the second variable indicating a duration of the optical axis scan processing for which the determination result that the detection area is in a second state is obtained, the second state being the other of the light entrance state and the light obstruction state, the value of the second variable being updated according to the determination that the detection area is in the second state (ST24, ST27); and notification control means for activating the malfunction notification means on a condition that the value of the first variable reaches a predetermined first reference value, and that, prior to this, a final value of the second variable is equal to or lower than a predetermined second reference value. optical axis scan processing, in which the optical axes are activated sequentially to detect the presence or absence of light entrance for the activated optical axes, and determination processing of determining whether a detection area formed by the optical axes is in a light entrance state or in a light obstruction state, based on a result of the optical axis scan processing, and malfunction notification means for notifying that an output indicating the determination result that the detection area is in the light entrance state or in the light obstruction state is due to a malfunction; characterized in that the multiple optical axis photoelectric sensor further comprises: variable update means for updating a first variable and a second variable according to the determination result of the optical axis scan processing (ST23, ST24, ST26, ST 27), the first variable indicating a duration of the optical axis scan processing for which the determination result that the detection area is in a first state is obtained, the first state being one of the light entrance state and the light obstruction state, the value of the first variable being updated as long as the determination continues that the detection area is in the first state (ST24, ST27), and the second variable indicating a duration of the optical axis scan processing for which the determination result that the detection area is in a second state is obtained, the second state being the other of the light entrance state and the light obstruction state, the value of the second variable being updated according to the determination that the detection area is in the second state (ST24, ST27); and notification control means for activating the malfunction notification means on a condition that the value of the first variable reaches a predetermined first reference value, and that, prior to this, a final value of the second variable is equal to or lower than a predetermined second reference value. variable update means for updating a first variable and a second variable according to the determination result of the optical axis scan processing (ST23, ST24, ST26, ST 27), the first variable indicating a duration of the optical axis scan processing for which the determination result that the detection area is in a first state is obtained, the first state being one of the light entrance state and the light obstruction state, the value of the first variable being updated as long as the determination continues that the detection area is in the first state (ST24, ST27), and the second variable indicating a duration of the optical axis scan processing for which the determination result that the detection area is in a second state is obtained, the second state being the other of the light entrance state and the light obstruction state, the value of the second variable being updated according to the determination that the detection area is in the second state (ST24, ST27); and notification control means for activating the malfunction notification means on a condition that the value of the first variable reaches a predetermined first reference value, and that, prior to this, a final value of the second variable is equal to or lower than a predetermined second reference value.