A position detector for a moving magnet type linear motor, the moving magnet type linear motor including: a stator with a plurality of coils placed in one direction; and a mover with a permanent magnet so placed as to be opposed to the stator, a magnetic field generated by applying a voltage to the plurality of coils of said stator causing said mover to move in said direction, the position detector detecting the position of the mover in the moving magnet type linear motor, the position detector comprising: a magnetic body fixed to said mover, and placed in a position to be opposed to a coil that is different from a coil opposed to said permanent magnet; power supply control means configured to select a pair of coils that hold the coil opposed to said magnetic body therebetween and generate a magnetic field for position detection by applying a voltage to the pair of coils selected on receipt of a first command; measuring means or measuring a current or a voltage induced in the coil that is held between the pair of coils on receipt of a second command; command means for giving the first command to said power supply control means and the second command to said measuring means; position determination means for determining the position of said magnetic body that changes in response to the position of said mover based on a measured value obtained by said measuring means, by controlling the command operation by said command means; voltage adjustment means for acquiring the measured value [Vvi] obtained by said measuring means, and for adjusting voltages [Vvo, Vwo] to be applied to said coils in a pair in such a way that the measured [Vvi] value obtained by said measuring means becomes a certain value by controlling said power supply control means based on the acquired measured value; and judgment means for acquiring the measured value [Vvi] obtained by said measuring means, and for determining whether or not the acquired measured value coincides with or is close to said certain value, when said judgment means judges that said measured value coincides with or is close to the certain value, said position determination means acquires the voltages applied to said coils in a pair from said power supply control means, and determines the position of said magnetic body based on the two acquired voltages [Vvo,Vwo]. a magnetic body fixed to said mover, and placed in a position to be opposed to a coil that is different from a coil opposed to said permanent magnet; power supply control means configured to select a pair of coils that hold the coil opposed to said magnetic body therebetween and generate a magnetic field for position detection by applying a voltage to the pair of coils selected on receipt of a first command; measuring means or measuring a current or a voltage induced in the coil that is held between the pair of coils on receipt of a second command; command means for giving the first command to said power supply control means and the second command to said measuring means; position determination means for determining the position of said magnetic body that changes in response to the position of said mover based on a measured value obtained by said measuring means, by controlling the command operation by said command means; voltage adjustment means for acquiring the measured value [Vvi] obtained by said measuring means, and for adjusting voltages [Vvo, Vwo] to be applied to said coils in a pair in such a way that the measured [Vvi] value obtained by said measuring means becomes a certain value by controlling said power supply control means based on the acquired measured value; and judgment means for acquiring the measured value [Vvi] obtained by said measuring means, and for determining whether or not the acquired measured value coincides with or is close to said certain value,