Disclosed is an electric motor-driven compressor having a structure capable of improving the performance of an electric motor of the electric motor-driven compressor for the vehicle. The electric motor-driven compressor has an angle which is formed by two straight lines passing through a center of the rotor and making contact with both end portions of one permanent magnet, and is in a range of about 48.7° to about 51°. The cogging torque and the torque ripples are minimized, the power of the electric motor is improved, and the electric motor is easily controlled.