A vibrator (3) is sandwiched between a base block (1) and a stator (2), and a substantially lower half of a substantially spherical rotor (6) is received in a recess (5) of the stator (2). A support member (7) is placed on an upper portion of the stator (2). A preload portion (10) is supported at an end of an angle portion (9) of the support member (7). A spherical member (11) rotatable about multiple axes of the preload portion (10) abuts against a top portion of the rotor (6) to apply a preload to the rotor (6). Driving the vibrator (3) rotates the rotor (6), whereby an output shaft (12) is moved between the preload portion (10) and an annular portion (8) of the support member (7) as a movable range.