A power transmission apparatus for vehicles for transmitting a driving force by coupling an input shaft (1) and an output shaft (2) of a hydraulic pump (3) to respective driving shafts of front and rear wheels of a four-wheel drive vehicle, wherein a throttle member (60) which is located on the axis of a rotor (30) and a casing interlocking respectively with the input and output shafts (1, 2), rotated with interlocking with one of the rotor (30) and casing and disposed movably along the axis to change the hydraulic fluid discharge passage area of the hydraulic pump (3) responsive to its movement, and a driving unit which includes a magnetic member (63) coupled coaxially to the throttle member (60) and a coil installed around the magnetic member (63) and supported nonrotatably, and moves the throttle member (60) by movement of the magnetic member (63) in connection with excitation of the coil (7) are provided.