Abstract: An indexing mechanism in a machine tool for selectively positioning plural pin portions of a crankshaft at the machining position aligned with the work spindle, wherein a indexing member engaging with the crankshaft through an engaging pin is rotated by an indexing motor through a gear train. The crankshaft is initially rotated in a first direction until a selected pin portion engages with a rest shoe of a rest device provided on the bed in order to be positioned in a reference angle position, in which the selected pin portion is located at the machining position aligned with a work spindle. The crankshaft is then clamped on the chucking device. After that, the indexing motor is rotated in a second direction opposite to the first direction until the load of the motor exceeds a reference level, so that the influence of a backlash in the gear train and a clearance between the engaging pin and the crankshaft is eliminated.