When a work implement is actuated in such a manner that a work point is located at each of a plurality of positions on a datum line, a first work point position computing section calculates a position of the work point at each of the plurality of positions. A calibration value computing section calculates calibration values of angle conversion parameters (αbm, βbm, αam, βam, αbk, βbk), dimension parameters (Lbm, Lam, Lbk), and line parameters (tilt tan θ, intercept Zline) using the fact that the positions of the work point at each of the plurality of positions calculated by the first work point position computing section can satisfy a linear equation indicating a datum line. A parameter update section reflects the calibration values calculated by the calibration value computing section in computation by a corresponding computing section that is one of the angle computing section and the first work point position computing section.