A power tool includes a tool bit, a tool holder, a bit holding member, a bit mounting hole, a through hole, an outside opening, a bit mounting hole side opening, an engaging member, a cylindrical operating member, a movement preventing portion, a biasing member, a first engaging region, a second engaging region, and a third engaging region. As the first, the second and the third engaging regions respectively cooperate, the tool bit can be automatically secured to the bit holding member by inserting the tool bit into the bit mounting hole of the bit holding member. Mounting and removing of the tool bit can be achieved without a ring spring.