The invention provides a turn signal switch device. Even if a control lever driven force is set with required strength, there's nothing to worry about the control lever base portion desquamation from a holder, assembly efficiency is fine and component amount can be reduced. When the turn signal switch device is assembled, a base portion (3a) of the control lever (3) is inserted into an opening (9a) of the holder (9), and a shaft (21) is inserted into a shaft hole (3c) of the base portion (3a) and a bearing hole (9e) of a side plate (9d) of the holder (9) so as to be retained. Then, the control lever (3) and the holder (9) are rotatably connected. Further, a ring-shaped groove (21b) is provided at the end of the shaft (21) opposite a head (21a), and a flexible engagement piece (9g) is provided on the side plate (9d) of the holder (9), the flexible engagement piece (9g) extending inward in the radial direction of the bearing hole (9e) so as to be engaged with the ring-shaped concave groove (21b). The flexible engagement piece (9g) is pressed and deflected by the leading end of the shaft (21) in the middle of attachment. Further, when the leading end passes through the flexible engagement piece (9g), the shaft (21) is snapped to the holder (9).