Provide is a position detection device or the like that can detect the position of the capsule endoscope with higher accuracy than before while cutting the calculation amount. An information processing device 6 includes: an existing region acquiring unit 621 that calculates a distance between each receiving antenna and a capsule endoscope based on each received strength of signals received by the receiving antennas and acquires a region where at least two of spheres, each with each receiving antenna as a center and the distance corresponding to each antenna as radii overlap with one another an orientation estimating unit 622 that estimates orientations of the capsule endoscope at points in the region based on positional relationships between the points and the receiving antennas, and received strength of signals received by the receiving antennas and a position determination unit 623 that determines the position of the capsule endoscope in the subject based on the positions of the points and the orientations of the capsule endoscope.
