A hydraulic excavator includes a base body portion, a movable portion, a hydraulic cylinder, a position sensor, a rotary encoder, and a control unit. The rotary encoder includes a light emitting unit, a light receiving unit, and a disk unit having a plurality of transmission portions. The control unit measures the stroke length of the hydraulic cylinder by correcting deviation of the stroke length, which is measured by the position sensor, based on the pulse signal output from the rotary encoder. In this way, there can be obtained a hydraulic excavator capable of precisely measuring a stroke length of a hydraulic cylinder driving a work implement, as well as a method for measuring the stroke of the hydraulic cylinder of the hydraulic excavator.