An object is to enable accurate position detection with a less calculation amount and at high speed, without being affected by an unnecessary magnetic field resulting from a guiding coil or the like arranged around a position detection area of a capsule medical device. The accurate position detection without being affected by an unnecessary second magnetic field can be realized by calculating the unnecessary second magnetic field induced and generated at positions of magnetic field sensors 41 1 to 41 n by a guiding coil 21 arranged around the position detection area of the medical device 10 due to an action of a first magnetic field generated by a magnetic field generator 30, at the time of position detection, and the second magnetic field is subtracted from the first magnetic field detected by the magnetic field sensors 41 1 to 41 n to calculate corrected magnetic-field information. Further, LUTs 52 x , 52 y , and 52 z that store beforehand numerical information having a correlation with the second magnetic field induced and generated at the positions of magnetic field sensors 41 1 to 41 n are used to calculate the second magnetic field, thereby enabling to reduce an amount of calculation performed each time and realize high speed processing.