A motor drive device comprising: an electric motor; and a control device located on an axial line of a rotary shaft of the electric motor and controlling driving of the electric motor, wherein the control device includes: a semiconductor switching element composing a bridge circuit for controlling current of the electric motor; a sensor board on which a rotational sensor for detecting a phase of a rotor of the electric motor is mounted; a capacitor assembly unit including a smoothing capacitor for suppressing a ripple component of current flowing through the electric motor; a power circuit including the semiconductor switching element; a heat sink for dissipating heat generated from the power circuit; and a control board on which a microcomputer for generating a drive signal for driving the semiconductor switching element is mounted, wherein the heat sink is located on the axial line of the rotary shaft of the electric motor, the power circuit is mounted on one surface of the heat sink perpendicular to the axial line of the rotary shaft of the electric motor, and the capacitor assembly unit is located on another surface parallel with the surface on which the power circuit is mounted, characterized in that the control device has the capacitor assembly unit located opposite to the power circuit via the heat sink, and the capacitor assembly unit is electrically connected to the power circuit via a bus bar penetrating through the heat sink. an electric motor; and a control device located on an axial line of a rotary shaft of the electric motor and controlling driving of the electric motor, wherein the control device includes: a semiconductor switching element composing a bridge circuit for controlling current of the electric motor; a sensor board on which a rotational sensor for detecting a phase of a rotor of the electric motor is mounted; a capacitor assembly unit including a smoothing capacitor for suppressing a ripple component of current flowing through the electric motor; a power circuit including the semiconductor switching element; a heat sink for dissipating heat generated from the power circuit; and a control board on which a microcomputer for generating a drive signal for driving the semiconductor switching element is mounted, wherein a semiconductor switching element composing a bridge circuit for controlling current of the electric motor; a sensor board on which a rotational sensor for detecting a phase of a rotor of the electric motor is mounted; a capacitor assembly unit including a smoothing capacitor for suppressing a ripple component of current flowing through the electric motor; a power circuit including the semiconductor switching element; a heat sink for dissipating heat generated from the power circuit; and a control board on which a microcomputer for generating a drive signal for driving the semiconductor switching element is mounted, wherein the heat sink is located on the axial line of the rotary shaft of the electric motor, the power circuit is mounted on one surface of the heat sink perpendicular to the axial line of the rotary shaft of the electric motor, and the capacitor assembly unit is located on another surface parallel with the surface on which the power circuit is mounted, characterized in that the control device has the capacitor assembly unit located opposite to the power circuit via the heat sink, and the capacitor assembly unit is electrically connected to the power circuit via a bus bar penetrating through the heat sink.