The position or the direction of a first marker which produces an alternating magnetic field by means of an external power supply is detected precisely even if the first marker coexists with a second marker which includes a resonance circuit having a resonance frequency the same as or close to the frequency of the alternating magnetic field. There is provided a position detection system (1) including a first marker (4) that produces a first alternating magnetic field having a single set of first position-calculating frequencies that are a predetermined frequency away from each other； a second marker (3) provided with a magnetic induction coil (5) having as a resonance frequency a substantially central frequency interposed between the single set of first position-calculating frequencies； a magnetic-field detection section (13) that is disposed outside the working region and that detects a magnetic field at the first position-calculating frequencies； an extracting section (30) that extracts from the detected magnetic field the sum of the intensities of a single set of first detection-magnetic-field components having the single set of first position-calculating frequencies； and a position/direction analyzing section (22) that calculates the position or the direction of the first marker (4) based on the extracted sum.
