Provided is a motor-driven compressor capable of realizing reduction in manufacturing costs. A compression mechanism of the motor-driven compressor according to the present invention includes a rotor rotatable by a rotation shaft and provided with a plurality of vane grooves, a plurality of vanes disposed advanceably and retractably in the respective vane grooves, a cup member formed into a bottomed cylindrical shape and enclosing the rotor, and a side plate closing an opening of the cup member The contour of the compressor is formed by a first housing and a second housing, and a suction pressure region in the first housing is hermetically closed from outside at a position where the first housing and the second housing are joined together.