The present invention provides a screwdriver which includes a shaft, a handle and a speed increasing mechanism, in which the speed increasing mechanism includes a central axle connected to the shaft and provided with a toothed part on its periphery, a first member is disposed in the interior of the handle, at least one gear is connected to the first member, and a geared sleeve is sheathed outside the gear, in which the inner side of the geared sleeve has teeth on corresponding positions, engaging with the gear which is disposed at a side part of the central axle and is engaged with the toothed part of the periphery of the central axle. The present invention also includes a locking mechanism addressing the problem of torque being not high.