A power transmission apparatus comprising: a clutch member housed in a clutch housing that rotates together with an input member that rotates with a driving force of an engine of a vehicle, the clutch housing having a plurality of driving clutch plates (6a, 6b, 6c) attached thereto, the clutch member including a first clutch member and a second clutch member, the first clutch member being connected to an output member that is able to rotate a wheel of the vehicle, the second clutch member having a plurality of driven clutch plates (7a, 7c) attached thereto, the driven clutch plates (7a, 7c) being arranged alternately with the driving clutch plates (6a, 6b, 6c); a pressure member movable between an operating position where the driving and driven clutch plates (6a, 6b, 6c, 7a, 7b, 7c) are pressed against each other so as to enable transmission of the driving force of the engine to the wheel and a non-operating position where a pressing force exerted on the driving and driven clutch plates (6a, 6b, 6c, 7a, 7b, 7c) is released so as to cut off transmission of the driving force of the engine to the wheel; a centrifugal clutch means including a weight member movable from a radially inner position to a radially outer position with centrifugal force produced by rotation of the clutch housing, the centrifugal clutch means being configured to, when the weight member is located at the radially outer position, press the driving and driven clutch plates (6a, 6b, 6c, 7a, 7b, 7c) against each other so as to enable transmission of the driving force of the engine to the wheel, the centrifugal clutch means being configured to, when the weight member is located at the radially inner position, release the pressing force exerted on the driving and driven clutch plates (6a, 6b, 6c, 7a, 7b, 7c) so as to cut off transmission of the driving force of the engine to the wheel; and a back torque transmission cam (K1, K2) that is able to, when the pressure member is located at the non-operating position, move the second clutch member so as to press the driving and driven clutch plates (6a, 6b, 6c, 7a, 7b, 7c) against each other upon reception of a rotational force by the first clutch member through the output member, characterized in that, the second clutch member presses all of the driving and driven clutch plates (6a, 6b, 6c, 7a, 7b, 7c) against each other during operation of the centrifugal clutch means and releases a pressing force exerted on some of the driving clutch plates located between the driven clutch plates attached to the second clutch member and driven clutch plates during operation of the back torque transmission cam (K1, K2). a clutch member housed in a clutch housing that rotates together with an input member that rotates with a driving force of an engine of a vehicle, the clutch housing having a plurality of driving clutch plates (6a, 6b, 6c) attached thereto, the clutch member including a first clutch member and a second clutch member, the first clutch member being connected to an output member that is able to rotate a wheel of the vehicle, the second clutch member having a plurality of driven clutch plates (7a, 7c) attached thereto, the driven clutch plates (7a, 7c) being arranged alternately with the driving clutch plates (6a, 6b, 6c); a pressure member movable between an operating position where the driving and driven clutch plates (6a, 6b, 6c, 7a, 7b, 7c) are pressed against each other so as to enable transmission of the driving force of the engine to the wheel and a non-operating position where a pressing force exerted on the driving and driven clutch plates (6a, 6b, 6c, 7a, 7b, 7c) is released so as to cut off transmission of the driving force of the engine to the wheel; a centrifugal clutch means including a weight member movable from a radially inner position to a radially outer position with centrifugal force produced by rotation of the clutch housing, the centrifugal clutch means being configured to, when the weight member is located at the radially outer position, press the driving and driven clutch plates (6a, 6b, 6c, 7a, 7b, 7c) against each other so as to enable transmission of the driving force of the engine to the wheel, the centrifugal clutch means being configured to, when the weight member is located at the radially inner position, release the pressing force exerted on the driving and driven clutch plates (6a, 6b, 6c, 7a, 7b, 7c) so as to cut off transmission of the driving force of the engine to the wheel; and a back torque transmission cam (K1, K2) that is able to, when the pressure member is located at the non-operating position, move the second clutch member so as to press the driving and driven clutch plates (6a, 6b, 6c, 7a, 7b, 7c) against each other upon reception of a rotational force by the first clutch member through the output member, characterized in that, the second clutch member presses all of the driving and driven clutch plates (6a, 6b, 6c, 7a, 7b, 7c) against each other during operation of the centrifugal clutch means and releases a pressing force exerted on some of the driving clutch plates located between the driven clutch plates attached to the second clutch member and driven clutch plates during operation of the back torque transmission cam (K1, K2).