An absolute displacement sensor 1 includes a sensor housing 2 serving as a detection object; a mass body 3 having a mass m which is movably supported by the sensor housing 2 with a spring coefficient k and a damping coefficient c; a detecting means 4 which electrically detects a relative velocity of the sensor housing 2 with respect to the mass body 3; a feedback control means 5 which controls the absolute displacement of the mass body 3 attributable to the absolute displacement of the sensor housing 2 by positively feeding back the relative displacement and by negatively feeding back a relative acceleration obtained by primarily differentiating the relative velocity, respectively; and a phase lag compensation means 6 which performs phase lag compensation with respect to the relative displacement.