To provide a feed screw mechanism of an electric motor capable of eliminating characteristic reduction in position control of a motor caused by viscosity of oil.
A shaft 32 for constituting the feed screw mechanism 1 of the electric motor is formed of metal, and a male screw 42 is formed on its peripheral surface. An out-fitting part 14 for constituting the feed screw mechanism 1 of the electric motor is formed of resin, and a female screw 43 is formed on its inner peripheral surface. An oil releasing groove 91 extending in the axial direction is arranged on a screw forming surface for forming the male screw 42, and one end of the oil releasing groove 91 is opened on a base end surface 93 of the shaft 32. Thus, a communicating space 101 communicating in the axial direction between the shaft 32 and the out-fitting part 14 is formed of the oil releasing groove 91, and the communicating space 101 is opened on the base end side of the feed screw mechanism 1 of the electric motor via an opening 102 of the base end surface 93.