A biosensor including light emitting elements and a light receiving element disposed on a principal surface of a wiring board a light shielding portion disposed between a light-emitting-element sealing portion and a light-receiving-element sealing portion a base medium having light transmitting properties, disposed in parallel with the wiring board with the light shielding portion therebetween an adhesion layer having light transmitting properties that bonds the base medium with the light-emitting-element sealing portion, the light-receiving-element sealing portion, and the light shielding portion and a first electrocardiograph electrode attached to a principal surface of the base medium. Both end portions of the adhesion layer and both end portions of the base medium are disposed such that they overlap neither of the light-receiving-element sealing portion nor the light-emitting-element sealing portion when viewed from a direction normal to the principal surface of the wiring board.
