Provided are a position detection apparatus for a capsule endoscope, having a constant accuracy while reducing a calculation amount, a capsule endoscope system including the position detection apparatus, and a position detecting program for the capsule endoscope. An information processor 6 includes a position information estimating unit 62 configured to calculate a first distance r n between each of a plurality of receiving antennas and the capsule endoscope based on each reception strength of a signal received by the plurality of receiving antennas, and configured to estimate, as a position of the capsule endoscope, a position where a total sum of distances from spherical surfaces is minimum inside a region where a plurality of spheres are overlapped. Each of the plurality of spheres has a center at each of the receiving antennas and has a radius of the distance r n for each of the receiving antennas.
