To provide an electrohydraulic servo motor having compact structure by improving the arrangement of a spool valve.

This electrohydraulic servo motor is provided with a main spool valve 54, which is arranged normal to an output shaft 34 and is moved in the axial direction by hydraulic pressure, and a pilot spool valve 52, which is engaged with the output shaft 34 and a revolving shaft 51 of a motor 50 so as to move in the axial direction through relative rotation of both shafts (34, 50) in order to regulate the supply/discharge of working oil through its movement in the axial direction, varying the hydraulic pressure acting on the main spool valve 54.