In this electric linear motion actuator, a linear motion mechanism and an electric motor are arranged in line along the same axis, which is an axis of a rotation input/output shaft of the linear motion mechanism. The electric motor includes a stator and a rotor which are arranged such that the directions of magnetic poles thereof for generating interlinkage magnetic flux contributing to a torque are parallel to a rotation shaft of a motor. The rotor has torque generating surfaces at both faces in the axial direction thereof. The stator has first and second excitation mechanisms arranged on both sides in the axial direction of the rotor. The first and second excitation mechanisms have independent first and second system coil groups. A power supply system for independently supplying power to the first and second system coil groups is provided.