PROBLEM TO BE SOLVED: To detect a faint optic element accurately in a biosensor provided with a light emitting element 24 and a light receiving element 26.SOLUTION: The biosensor includes a board 22 that has optical transparency, the light emitting element 24 that is provided on a mounting face side of the board 22 and emits light, and the light receiving element 26 that is provided on a non-mounting face side of the board 22 and receives reflected light from a living body among the light emitted from light emitting element 24 to output a signal corresponding to the light reception. That is, the light receiving element 26 is provided for the board 22 on its non-mounting surface side opposite to the mounting surface side where the light emitting element 24 is provided, and is set back from a light emitting surface at a distance equal to or more than the thickness of the board 22.COPYRIGHT: (C)2013,JPO&INPIT【課題】発光素子24と受光素子26とを備える生体センサーにおいて微弱な光成分を精度良く検出する。【解決手段】光透過性を有する基板22と、基板22の装着面側に設けられ、光を出射する発光素子24と、基板22の非装着面側に設けられ、発光素子24から出射した光のうち、生体からの反射光を受光して、当該受光に応じた信号を出力する受光素子26とを備える構成とする。すなわち、受光素子26を、基板22に対して発光素子24が設けられた装着面側とは反対側の非装着面側に設けて、発光面から基板22の厚さ以上の距離で奥まったところに位置させる。【選択図】図3