A probe straightness measuring method includes: placing a measurement jig having a measurement reference surface with a known profile error on a stage surface of an XY stage so that the measurement reference surface is slanted in a moving direction of the XY stage; measuring a displaced position of the measurement piece by a displacement detector of the probe each time the XY stage is moved for a predetermined distance while controlling a driving actuator so that the measurement piece of a probe touches the measurement reference surface at a constant pressure; and calculating a straightness error of a measurement-piece moving mechanism on a basis of a measured position of the measurement piece obtained in the measuring, a nominal position of the measurement piece obtained by a calculation and a slant angle of the measurement reference surface.