A biosensor comprising: a wiring board ; a light emitting element and a light receiving element disposed on a principal surface of the wiring board with a predetermined spacing between the light emitting element and the light receiving element; a light-emitting-element sealing portion having light transmitting properties and configured to seal the light emitting element ; a light-receiving-element sealing portion having light transmitting properties and configured to seal the light receiving element ; a light shielding portion disposed between the light-emitting-element sealing portion and the light-receiving-element sealing portion ; and a cover having light transmitting properties, disposed in parallel with the wiring board with the light shielding portion therebetween, wherein the light-emitting-element sealing portion and the light-receiving-element sealing portion each have a first surface disposed on the principal surface of the wiring board , and the first surface of the light-emitting-element sealing portion abuts the light-emitting-element, and the first surface of the light-receiving-element sealing portion abuts the light-receiving-element; wherein an end portion of the cover closer to the light receiving element is disposed such that the end portion does not overlap the light-receiving-element sealing portion when viewed from a direction normal to the principal surface of the wiring board , and/or wherein an end portion of the cover closer to the light emitting element is disposed such that the end portion does not overlap the light-emitting-element sealing portion when viewed from a direction normal to the principal surface of the wiring board . a wiring board ; a light emitting element and a light receiving element disposed on a principal surface of the wiring board with a predetermined spacing between the light emitting element and the light receiving element; a light-emitting-element sealing portion having light transmitting properties and configured to seal the light emitting element ; a light-receiving-element sealing portion having light transmitting properties and configured to seal the light receiving element ; a light shielding portion disposed between the light-emitting-element sealing portion and the light-receiving-element sealing portion ; and a cover having light transmitting properties, disposed in parallel with the wiring board with the light shielding portion therebetween, wherein the light-emitting-element sealing portion and the light-receiving-element sealing portion each have a first surface disposed on the principal surface of the wiring board , and the first surface of the light-emitting-element sealing portion abuts the light-emitting-element, and the first surface of the light-receiving-element sealing portion abuts the light-receiving-element; wherein an end portion of the cover closer to the light receiving element is disposed such that the end portion does not overlap the light-receiving-element sealing portion when viewed from a direction normal to the principal surface of the wiring board , and/or wherein an end portion of the cover closer to the light emitting element is disposed such that the end portion does not overlap the light-emitting-element sealing portion when viewed from a direction normal to the principal surface of the wiring board . <EOS>