Distances from three displacement meters arranged in a first direction to three measuring points arranged along a measurement line that extends in the first direction on a surface of an object to be measured are measured while a movable body, which is either the three displacement meter or an object to be measured, is moved in the first direction relative to a stationary body, which is the other one. Solution candidates are determined which are defined by two profiles among a surface profile along the measurement line, a profile of locus curve which is the locus a reference point fixed to the movable body, and a profile of a pitching component accompanied with the movement of the movable body. One candidate solution with the highest fitness is extracted by applying a genetic algorithm using a fitness function defined on the basis of the other profile.