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 each have a second surface, wherein the cover is attached to the second surface; wherein the light-emitting-element sealing portion and/or the light-receiving-element sealing portion is formed from a translucent resin; and, wherein the light emitting element and the light receiving element are disposed at either end of a longitudinal axis of the biosensor, characterized in that the cover is divided into first and second cover members with a spacing therebetween, the spacing extending in a lateral direction of the biosensor at 50° or less to the longitudinal axis of the biosensor, the first cover member positioned closer to the light emitting element and the second cover member positioned closer to the light receiving element. 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 each have a second surface, wherein the cover is attached to the second surface; wherein the light-emitting-element sealing portion and/or the light-receiving-element sealing portion is formed from a translucent resin; and, wherein the light emitting element and the light receiving element are disposed at either end of a longitudinal axis of the biosensor, characterized in that the cover is divided into first and second cover members with a spacing therebetween, the spacing extending in a lateral direction of the biosensor at 50° or less to the longitudinal axis of the biosensor, the first cover member positioned closer to the light emitting element and the second cover member positioned closer to the light receiving element. <EOS>