A drive source unit (62) is disposed in a base portion (32) of an endoscope. The drive source unit (62) includes a first frame (112), a second frame (114), a motor (116), a gear box (118) and a potentiometer (120). The gear box (118) includes a horizontal power transmission mechanism (118a) for horizontally transmitting power from the motor (116), and an epicyclic gear mechanism (118b, 118c) for vertically transmitting power from the horizontal power transmission mechanism (118a). Thus, the power from the motor (116) can be output from the opposite side of the motor (116), such that the space of the base portion (32) can be reduced.
