A power transmission device comprising: a rotating shaft ; a housing configured by a conductive material and rotatably supporting the rotating shaft ; an oil seal disposed in a gap between the rotating shaft and the housing ; and an oil leak detection device disposed outside of the oil seal in an axial direction parallel to an axial center (AX) 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 attached to the housing and having an N-pole and an S-pole that face each other; a plurality of commutators attached to the rotating shaft ; a coil wound onto the rotating shaft on an inside of the pair of permanent magnets in a radial direction centered on the axial center (AX) of the rotating shaft , and electrically connected to the plurality of commutators ; a pair of brushes that are attached to the housing and capable of coming into contact with each of the plurality of commutators ; wherein the pair of brushes 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 and the housing . a rotating shaft ; a housing configured by a conductive material and rotatably supporting the rotating shaft ; an oil seal disposed in a gap between the rotating shaft and the housing ; and an oil leak detection device disposed outside of the oil seal in an axial direction parallel to an axial center (AX) 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 attached to the housing and having an N-pole and an S-pole that face each other; a plurality of commutators attached to the rotating shaft ; a coil wound onto the rotating shaft on an inside of the pair of permanent magnets in a radial direction centered on the axial center (AX) of the rotating shaft , and electrically connected to the plurality of commutators ; a pair of brushes that are attached to the housing and capable of coming into contact with each of the plurality of commutators ; wherein the pair of brushes 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 and the housing . a pair of permanent magnets attached to the housing and having an N-pole and an S-pole that face each other; a plurality of commutators attached to the rotating shaft ; a coil wound onto the rotating shaft on an inside of the pair of permanent magnets in a radial direction centered on the axial center (AX) of the rotating shaft , and electrically connected to the plurality of commutators ; a pair of brushes that are attached to the housing and capable of coming into contact with each of the plurality of commutators ; wherein the pair of brushes 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 and the housing . <EOS>