A truing device of a grinding machine includes: a truer that corrects a shape of a grinding wheel; a swivel table that supports the truer such that the truer is swivelable about a swivel axis Ac; detecting means for directly detecting a distance from a truing edge position of the truer, which contacts the grinding wheel during correction of the shape of the grinding wheel, to a swivel center O of the swivel table; and control means for controlling the truing edge position of the truer with respect to the grinding wheel based on the distance L detected by the detecting means to true the grinding wheel.