A power transmission apparatus comprising: a clutch member (4a, 4b) 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 attached thereto, the clutch member (4a, 4b) having a plurality of driven clutch plates attached thereto, the driven clutch plates being arranged alternately with the driving clutch plates, the clutch member (4a, 4b) being connected to an output member that is able to rotate a wheel of the vehicle; a pressure member movable between an operating position where the driving and driven clutch plates (6, 7) 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 (6, 7) 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 (6, 7) against each other so as to enable transmission of the driving force of the engine to the wheel and 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 (6, 7) so as to cut off transmission of the driving force of the engine to the wheel; and a pressing assist cam to increase the pressing force exerted on the driving and driven clutch plates (6, 7), characterized in that, the pressing assist cam includes an inclined surface of the clutch member (4a, 4b) and an inclined surface of the pressure member that face each other, in course of movement of the weight member of the centrifugal clutch means from the radially inner position to the radially outer position and a resulting increase in torque transmitted from the input member to the output member, the apparatus includes a first torque region (α1) where the apparatus restricts operation of the pressing assist cam and a second torque region (α2) where the apparatus allows operation of the pressing assist cam. a clutch member (4a, 4b) 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 attached thereto, the clutch member (4a, 4b) having a plurality of driven clutch plates attached thereto, the driven clutch plates being arranged alternately with the driving clutch plates, the clutch member (4a, 4b) being connected to an output member that is able to rotate a wheel of the vehicle; a pressure member movable between an operating position where the driving and driven clutch plates (6, 7) 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 (6, 7) 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 (6, 7) against each other so as to enable transmission of the driving force of the engine to the wheel and 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 (6, 7) so as to cut off transmission of the driving force of the engine to the wheel; and a pressing assist cam to increase the pressing force exerted on the driving and driven clutch plates (6, 7), characterized in that, the pressing assist cam includes an inclined surface of the clutch member (4a, 4b) and an inclined surface of the pressure member that face each other, in course of movement of the weight member of the centrifugal clutch means from the radially inner position to the radially outer position and a resulting increase in torque transmitted from the input member to the output member, the apparatus includes a first torque region (α1) where the apparatus restricts operation of the pressing assist cam and a second torque region (α2) where the apparatus allows operation of the pressing assist cam.