A stroke operation diagnosis supporting device for a hydraulic cylinder includes: movable portions; hydraulic cylinders; a stroke sensor measuring a stroke length of the hydraulic cylinder; a reset sensor measuring a reset reference point at which a measurement value of the stroke length obtained by the stroke sensor is reset; a stroke end detection process unit detecting a stroke end position of the hydraulic cylinder; a calibration process unit calibrating the measurement value of the stroke length upon the detection of the reset reference point and/or the stroke end position; and a monitor displaying on a screen at least the measurement value of the stroke length obtained by the stroke sensor and a calibration state obtained by the calibration process unit, wherein the monitor displays continuous time change of the measurement value of the stroke length obtained by the stroke sensor.