A starter includes a motor section; an output shaft which rotates with receiving a rotational force of the motor section; a gear mechanism which transmits the rotational force of the output shaft to a ring gear of an engine; and a switch unit which performs electrical connection and disconnection to the motor section. Thus, the output shaft, the gear mechanism and the switch unit are accommodated in a housing, and a groove section for weakening the stiffness of the housing is formed in housing at a position which avoids a position where the switch unit is arranged.