A proximity sensor for detecting presence or absence of a metal body or a position of the metal body using a magnetic field, said proximity sensor comprising: a light-blocking housing having an elongated cylindrical shape and including a front end and a rear end in an axial direction; a detecting coil located at the front end within said light-blocking housing; a circuit board in a shape of a flat plate, said circuit board being provided with a processing circuit electrically connected to said detecting coil and disposed behind said detecting coil so as to extend along the axial direction of said light-blocking housing; a light emitting device mounted on one of main surfaces of said circuit board and being adapted to emit light in accordance with an operation state; and a light-transmitting cylindrical light guide surrounding, along a circumferential direction of said light-blocking housing, a portion of said circuit board having said light emitting device mounted thereon, said light-transmitting cylindrical light guide being adapted to guide outgoing light from said light emitting device to be emitted to outside, characterized in said light-transmitting cylindrical light guide including a first light outgoing region for causing the light emitted from said light emitting device to pass therethrough and for directly emitting the light to outside, a reflective surface (43a1) for reflecting the light emitted from said light emitting device to guide the light through said light-transmitting cylindrical light guide in the circumferential direction, and a second light outgoing region (43a2) for emitting, to outside, the light reflected on said reflective surface (43a1) and propagated through said light-transmitting cylindrical light guide, wherein said first light outgoing region is provided in a portion of an outer circumferential surface of said light-transmitting cylindrical light guide covering said one of the main surfaces of said circuit board on which said light emitting device is mounted, and said second light outgoing region (43a2) is provided in a portion of the outer circumferential surface of said light-transmitting cylindrical light guide blocked by said circuit board as seen from said light emitting device. a light-blocking housing having an elongated cylindrical shape and including a front end and a rear end in an axial direction; a detecting coil located at the front end within said light-blocking housing; a circuit board in a shape of a flat plate, said circuit board being provided with a processing circuit electrically connected to said detecting coil and disposed behind said detecting coil so as to extend along the axial direction of said light-blocking housing; a light emitting device mounted on one of main surfaces of said circuit board and being adapted to emit light in accordance with an operation state; and a light-transmitting cylindrical light guide surrounding, along a circumferential direction of said light-blocking housing, a portion of said circuit board having said light emitting device mounted thereon, said light-transmitting cylindrical light guide being adapted to guide outgoing light from said light emitting device to be emitted to outside, characterized in said light-transmitting cylindrical light guide including a first light outgoing region for causing the light emitted from said light emitting device to pass therethrough and for directly emitting the light to outside, a reflective surface (43a1) for reflecting the light emitted from said light emitting device to guide the light through said light-transmitting cylindrical light guide in the circumferential direction, and a second light outgoing region (43a2) for emitting, to outside, the light reflected on said reflective surface (43a1) and propagated through said light-transmitting cylindrical light guide, wherein said first light outgoing region is provided in a portion of an outer circumferential surface of said light-transmitting cylindrical light guide covering said one of the main surfaces of said circuit board on which said light emitting device is mounted, and said second light outgoing region (43a2) is provided in a portion of the outer circumferential surface of said light-transmitting cylindrical light guide blocked by said circuit board as seen from said light emitting device.