To provide a lower-cost adapter for assisting screwdriver rotation.

The adapter for assisting screwdriver rotation includes: a grip 1 in contact with a palm of a user's hand; a shaft 2 rotatably attached to the grip 1; a fixed part 4 attached to the shaft 2; a mounting part 10 provided at the tip of the fixed part 4 so as to make a screwdriver chip 7 removably mounted thereto in an extending direction of the shaft 2; and a protrusion 5 formed around the fixed part 4 and held by fingers when the screwdriver chip 7 is rotated. The mounting part 10 has: a recess 43 for making a part of the screwdriver chip 7 inserted thereto; each screw hole 44 formed at the inner-wall surface of the recess 43; and each bolt 8 screwed into each screw hole 44 so as to fix a part of the screwdriver chip 7 inserted to the recess 43.