A position detecting system (1; 1a; 41), comprising: a magnetic field generator configured to generate a magnetic field in a three-dimensional space; a detecting body (2; 42) that incorporates a resonance circuit for resonating with the magnetic field of the magnetic field generator to generate a resonance magnetic field, a current bypass circuit connected to the resonance circuit in parallel to form an alternative path of a current in the resonance circuit, and a resonance control circuit (24b; 64b) for controlling a current flow through the current bypass circuit to switch a resonant state and a non-resonant state of the resonance circuit, and is introduced into the three-dimensional space; a magnetic field detector configured to detect an environmental magnetic field, being a magnetic field in the three-dimensional space excluding the resonance magnetic field, and including at least a magnetic field of the magnetic field generator if the resonance circuit is in the non-resonant state, and configured to detect a spatial magnetic field in the three-dimensional space including the environmental magnetic field and the resonance magnetic field if the resonance circuit is in the resonant state; a position/direction calculating unit configured to perform position/direction calculating processing for calculating a position and a direction of the detecting body (2; 42) based on the detection data of the resonance magnetic field obtained by subtracting the detection data of the environmental magnetic field from the detection data of the spatial magnetic field; and a control unit (19; 59) configured to acquire detection data of the environmental magnetic field to perform update processing on the detection data of the environmental magnetic field if the resonance circuit is in the non-resonant state, to acquire the detection data of the spatial magnetic field if the resonance circuit is in the resonant state, and to cause the position/direction calculating unit to execute the position/direction calculating processing using the detection data of the spatial magnetic field thus acquired and the detection data of the environmental magnetic field which is subjected to the update processing. a magnetic field generator configured to generate a magnetic field in a three-dimensional space; a detecting body (2; 42) that incorporates a resonance circuit for resonating with the magnetic field of the magnetic field generator to generate a resonance magnetic field, a current bypass circuit connected to the resonance circuit in parallel to form an alternative path of a current in the resonance circuit, and a resonance control circuit (24b; 64b) for controlling a current flow through the current bypass circuit to switch a resonant state and a non-resonant state of the resonance circuit, and is introduced into the three-dimensional space; a magnetic field detector configured to detect an environmental magnetic field, being a magnetic field in the three-dimensional space excluding the resonance magnetic field, and including at least a magnetic field of the magnetic field generator if the resonance circuit is in the non-resonant state, and configured to detect a spatial magnetic field in the three-dimensional space including the environmental magnetic field and the resonance magnetic field if the resonance circuit is in the resonant state; a position/direction calculating unit configured to perform position/direction calculating processing for calculating a position and a direction of the detecting body (2; 42) based on the detection data of the resonance magnetic field obtained by subtracting the detection data of the environmental magnetic field from the detection data of the spatial magnetic field; and a control unit (19; 59) configured to acquire detection data of the environmental magnetic field to perform update processing on the detection data of the environmental magnetic field if the resonance circuit is in the non-resonant state, to acquire the detection data of the spatial magnetic field if the resonance circuit is in the resonant state, and to cause the position/direction calculating unit to execute the position/direction calculating processing using the detection data of the spatial magnetic field thus acquired and the detection data of the environmental magnetic field which is subjected to the update processing.