A biosensor (100) includes: light emitting elements (121, 122) and a light receiving element (123) disposed on a principal surface (160a) of a wiring board (160)； a light shielding portion (173) disposed between a light-emitting-element sealing portion (171) and a light-receiving-element sealing portion (172)； a base medium (151) having light transmitting properties, disposed in parallel with the wiring board (160) with the light shielding portion (173) therebetween； an adhesion layer (180) having light transmitting properties, configured to bond the base medium (151) with the light-emitting-element sealing portion (171), the light-receiving-element sealing portion (172), and the light shielding portion (173)； and a first electrocardiograph electrode (130) attached to a principal surface (151a) of the base medium (151). Both end portions (184 and 185) of the adhesion layer (180) and both end portions (154 and 155) of the base medium (151) are disposed such that they overlap neither of the light-receiving-element sealing portion (172) nor the light-emitting-element sealing portion (171) when viewed from a direction (10) normal to the principal surface (160a) of the wiring board (160).
