The screw tightening apparatus includes a motor, an output shaft to which a bit for screw tightening is connected so as to be rotatable integrally with the output shaft and which is axially movable, the output shaft being driven to be rotated by the motor, a spring whose one end contacts a member constituting a main body of the screw tightening apparatus, and a spring receiving member which the other end of the spring contacts and transmits a biasing force of the spring to the output shaft. The screw tightening apparatus further includes a conductive member which contacts the output shaft and the spring receiving member. This configuration enables static electricity generated on the bit to certainly flow into the main body of the apparatus (ground) via the output shaft, the conductive member, the spring receiving member, and the spring.