An absolute position measuring device comprising: a main body comprising a through hole, with a female screw provided around the inner periphery at one end of the through hole; a movable member, wherein said movable member is a spindle having an axis and provided to be movable forth or back by rotation in an axial direction thereof by engagement between the female screw of the main body and a feed screw of the spindle; a phase signal originating section (3A, 3B) for originating two or more phase signals of different periods in accordance with an amount of movement of said movable member, said phase signal originating section (3A, 3B) comprises two rotary encoders (3A, 3B) having a stator fixed to said main body and a rotor (5A, 5B) opposed to said stator and provided rotatably in conjunction with the rotation of said spindle; and an arithmetical operation section for making an arithmetical operation on said phase signals to obtain an absolute position of said movable member, said arithmetical operation section including a phase signal processing section for comparing said phase signals to obtain a phase difference (ΔΘ) between said phase signals, and an absolute position calculating section for calculating the absolute position of said movable member from the phase difference obtained by said phase signal processing section, wherein said spindle is inserted independently rotatably through a center of rotation of said rotor (5A, 5B) and has two key grooves (23A, 23B) provided around the outer periphery of said spindle, said two rotors (5A, 5B) are provided with keys (55A, 55B) engaging said key grooves (23A, 23B), and said two key grooves (23A, 23B) are provided such that said two rotors (5A, 5B) have different rotational periods, and a different phase difference at a different position of said spindle in the movable area of said spindle. a main body comprising a through hole, with a female screw provided around the inner periphery at one end of the through hole; a movable member, wherein said movable member is a spindle having an axis and provided to be movable forth or back by rotation in an axial direction thereof by engagement between the female screw of the main body and a feed screw of the spindle; a phase signal originating section (3A, 3B) for originating two or more phase signals of different periods in accordance with an amount of movement of said movable member, said phase signal originating section (3A, 3B) comprises two rotary encoders (3A, 3B) having a stator fixed to said main body and a rotor (5A, 5B) opposed to said stator and provided rotatably in conjunction with the rotation of said spindle; and an arithmetical operation section for making an arithmetical operation on said phase signals to obtain an absolute position of said movable member, said arithmetical operation section including a phase signal processing section for comparing said phase signals to obtain a phase difference (ΔΘ) between said phase signals, and an absolute position calculating section for calculating the absolute position of said movable member from the phase difference obtained by said phase signal processing section, wherein said spindle is inserted independently rotatably through a center of rotation of said rotor (5A, 5B) and has two key grooves (23A, 23B) provided around the outer periphery of said spindle, said two rotors (5A, 5B) are provided with keys (55A, 55B) engaging said key grooves (23A, 23B), and said two key grooves (23A, 23B) are provided such that said two rotors (5A, 5B) have different rotational periods, and a different phase difference at a different position of said spindle in the movable area of said spindle.