The present invention provides a sample holding carrier that can accurately measure a sample with a simple configuration, and a fluorescence detection system and device that use the same. Biosensor substrate includes: base substrate on which excitation light is incident from a lower surface; reflecting film that is arranged on an upper surface of base substrate to partially reflect the excitation light; and plural wells that are arranged on an upper surface side of reflecting film and have bottom surface portions. The excitation light is converged to be incident on base substrate. Distance from reflecting surface that is of a boundary between reflecting film and base substrate to bottom surface portion of well is less than or equal to a focal depth of the excitation light. Therefore, the sample accommodated in bottom surface portion of well can surely and efficiently be irradiated with the excitation light, and accurately be measured.