PURPOSE: To make an actuator compact and lightweight by forming the motor shaft of a motor built into an actuator, and a drive force transmission shaft for transmitting a drive force to a table mechanism, as integrated with each other.

CONSTITUTION: When a motor 84 is driven for rotation, a vibration generated due to a ball screw shaft 80 is absorbed by the first bearing member 104, thereby preventing the vibration from being transmitted to a drive shaft 102. Also, when displacement due to a difference in thermal expansion between a frame 98 and the drive shaft 102 is generated due to heat generated in a motor section 92, a spring washer 110 is elastically deformed to absorb the displacement. As a result, the loading of axial stress on the first bearing member 104 is prevented. On the other hand, the second bearing member 108 absorbs an axial load and another load in a direction orthogonal with an axial line.