To provide a screwdriver capable of transmitting torque by preventing removal of the screwdriver from a groove of a fastener by a cam effect.

This screwdriver has a handle part and a recessed part type engaging part formed on an end of the handle part, the recessed part type engaging part has a central core 54 and a plurality of blades 52 radially extended from the central core, each of the blades has at least one driving force transmitting wall 64 and a wall near the outer edge side, at least one rib 60 formed on at least one of driving force transmitting wall surfaces of at least one of wing parts is orientated to actually vertically extend to the wall near the outer edge side of the blade, and at least one of the ribs is constituted so that a cross-section area is reduced toward a direction of the inner edge side along the radial direction.