A power transmission device comprising: a generator that is driven by power of an internal combustion engine; a drive motor that is driven by electric power generated by the generator; and a drive wheel that is driven by the power of the internal combustion engine or by the power of the drive motor, characterized in that: a first power transmission path is provided to transmit power between the drive motor and the drive wheel, a first clutch mechanism is provided with a first sleeve that is engaged or disengaged so as to connect or disconnect power transmission of the first power transmission path, a second power transmission path is provided to transmit power between the internal combustion engine and the drive wheel, a second clutch mechanism is provided with a second sleeve that is engaged or disengaged so as to connect or disconnect power transmission of the second power transmission path, and a shift cam mechanism is provided that is actuated by a mode actuator, the shift cam mechanism is configured to switch between engagement and disengagement of the first clutch mechanism and the second clutch mechanism, and has a first cam groove (61, 61a, 61b) and a second cam groove (62, 62a, 62b) into which the first sleeve and the second sleeve are respectively fitted, the first cam groove and the second cam groove of the shift cam mechanism are configured to move the first sleeve and the second sleeve, and have a first series mode position in which the first clutch mechanism is engaged and the second clutch mechanism is disengaged, a parallel mode position in which the first clutch mechanism is engaged and the second clutch mechanism is engaged, an internal combustion engine direct connection mode position in which the first clutch mechanism is disengaged and the second clutch mechanism is engaged, a neutral mode position in which the first clutch mechanism is disengaged and the second clutch mechanism is disengaged, and a second series mode position in which the first clutch mechanism is engaged and the second clutch mechanism is disengaged, and the first series mode position, the parallel mode position, the internal combustion engine direct connection mode, the neutral mode position, and the second series mode position are arranged in that order. a generator that is driven by power of an internal combustion engine; a drive motor that is driven by electric power generated by the generator; and a drive wheel that is driven by the power of the internal combustion engine or by the power of the drive motor, characterized in that: a first power transmission path is provided to transmit power between the drive motor and the drive wheel, a first clutch mechanism is provided with a first sleeve that is engaged or disengaged so as to connect or disconnect power transmission of the first power transmission path, a second power transmission path is provided to transmit power between the internal combustion engine and the drive wheel, a second clutch mechanism is provided with a second sleeve that is engaged or disengaged so as to connect or disconnect power transmission of the second power transmission path, and a shift cam mechanism is provided that is actuated by a mode actuator, the shift cam mechanism is configured to switch between engagement and disengagement of the first clutch mechanism and the second clutch mechanism, and has a first cam groove (61, 61a, 61b) and a second cam groove (62, 62a, 62b) into which the first sleeve and the second sleeve are respectively fitted, a first power transmission path is provided to transmit power between the drive motor and the drive wheel, a first clutch mechanism is provided with a first sleeve that is engaged or disengaged so as to connect or disconnect power transmission of the first power transmission path, a second power transmission path is provided to transmit power between the internal combustion engine and the drive wheel, a second clutch mechanism is provided with a second sleeve that is engaged or disengaged so as to connect or disconnect power transmission of the second power transmission path, and a shift cam mechanism is provided that is actuated by a mode actuator, the shift cam mechanism is configured to switch between engagement and disengagement of the first clutch mechanism and the second clutch mechanism, and has a first cam groove (61, 61a, 61b) and a second cam groove (62, 62a, 62b) into which the first sleeve and the second sleeve are respectively fitted, the first cam groove and the second cam groove of the shift cam mechanism are configured to move the first sleeve and the second sleeve, and have a first series mode position in which the first clutch mechanism is engaged and the second clutch mechanism is disengaged, a parallel mode position in which the first clutch mechanism is engaged and the second clutch mechanism is engaged, an internal combustion engine direct connection mode position in which the first clutch mechanism is disengaged and the second clutch mechanism is engaged, a neutral mode position in which the first clutch mechanism is disengaged and the second clutch mechanism is disengaged, and a second series mode position in which the first clutch mechanism is engaged and the second clutch mechanism is disengaged, and the first series mode position, the parallel mode position, the internal combustion engine direct connection mode, the neutral mode position, and the second series mode position are arranged in that order.