To resolve the problem of the damageability of gear trains in the cases of gearings for fastening tools especially when using impact wrenches as the fastening tools.

This gearing for fastening tools houses in its case 1 a gear train including a plurality of transmission gears 3, 5, 7, ..., connected one to the next with idle gears interposed therebetween, each of which transmission gears has a fitting hole 29 in which are releasable fitted fastening-tool drive ends or sockets for such fasteners as bolts and nuts. The idle gears are placed in a set of two, as indicated at 13a, 13b, 15a, 15b,..., between every two adjacent transmission gears.