PURPOSE: To easily tighten a nut of a PC steel bar even in a narrow space of a longitudinal hole.

CONSTITUTION: In a PC steel bar tightening device 10 comprising a drive side gear 12 having a torque wrench fitting hole 15, a driven side gear 13 for engagement with the gear 12, and a fixing nut 14 in threaded engagement with a PC steel bar 19, a torque wrench 22 is fitted into the gear 12, while the gear 13 is operatively connected to the nut 14 in threaded engagement with the PC steel bar. Since turning forces of the torque wrench are transmitted to the nut 14 through the gear 12, the torque wrench is fitted into the gear 12 from the outside of a longitudinal hole 18 so that the torque wrench is turned, whereby the turning forces are transmitted through the gears 12 and 13 to the nut 14, thereby tightening the nut 14 and the PC steel bar.