A power transmission device comprising: a rotating shaft; a housing configured by a conductive material and rotatably supporting the rotating shaft; an oil seal (35, 38) disposed in a gap between the rotating shaft and the housing; and an oil leak detection device disposed outside of the oil seal (35, 38) in an axial direction parallel to an axial center of the rotating shaft, wherein the oil leak detection device has a current sensor configured to detect a current, characterized in that the oil leak detection device further comprises: a pair of permanent magnets (51, 52) attached to the housing and having an N-pole and an S-pole that face each other; a plurality of commutators (53, 54) attached to the rotating shaft; a coil wound onto the rotating shaft on an inside of the pair of permanent magnets (51, 52) in a radial direction centered on the axial center of the rotating shaft, and electrically connected to the plurality of commutators (53, 54); a pair of brushes (56, 57) that are attached to the housing and capable of coming into contact with each of the plurality of commutators (53, 54); wherein the pair of brushes (56, 57) are attached to the housing through an insulative oil absorbing material; and wherein the current sensor is configured to detect an induction current flowing between the pair of brushes (56, 57) and the housing. a rotating shaft; a housing configured by a conductive material and rotatably supporting the rotating shaft; an oil seal (35, 38) disposed in a gap between the rotating shaft and the housing; and an oil leak detection device disposed outside of the oil seal (35, 38) in an axial direction parallel to an axial center of the rotating shaft, wherein the oil leak detection device has a current sensor configured to detect a current, characterized in that the oil leak detection device further comprises: a pair of permanent magnets (51, 52) attached to the housing and having an N-pole and an S-pole that face each other; a plurality of commutators (53, 54) attached to the rotating shaft; a coil wound onto the rotating shaft on an inside of the pair of permanent magnets (51, 52) in a radial direction centered on the axial center of the rotating shaft, and electrically connected to the plurality of commutators (53, 54); a pair of brushes (56, 57) that are attached to the housing and capable of coming into contact with each of the plurality of commutators (53, 54); wherein the pair of brushes (56, 57) are attached to the housing through an insulative oil absorbing material; and wherein the current sensor is configured to detect an induction current flowing between the pair of brushes (56, 57) and the housing. a pair of permanent magnets (51, 52) attached to the housing and having an N-pole and an S-pole that face each other; a plurality of commutators (53, 54) attached to the rotating shaft; a coil wound onto the rotating shaft on an inside of the pair of permanent magnets (51, 52) in a radial direction centered on the axial center of the rotating shaft, and electrically connected to the plurality of commutators (53, 54); a pair of brushes (56, 57) that are attached to the housing and capable of coming into contact with each of the plurality of commutators (53, 54); wherein the pair of brushes (56, 57) are attached to the housing through an insulative oil absorbing material; and wherein the current sensor is configured to detect an induction current flowing between the pair of brushes (56, 57) and the housing.