A biosensor (200, 300) comprising: a wiring board (260, 360); a light emitting element (221, 222, 321, 322) and a light receiving element (223, 323) 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 (271, 371) having light transmitting properties and configured to seal the light emitting element (221, 222, 321, 322); a light-receiving-element sealing portion (272, 372) having light transmitting properties and configured to seal the light receiving element (223, 323); a light shielding portion (273, 373) disposed between the light-emitting-element sealing portion (271, 371) and the light-receiving-element sealing portion (272, 372); and a cover (290, 390) having light transmitting properties, disposed in parallel with the wiring board (260, 360) with the light shielding portion (273, 373) therebetween, wherein the light-emitting-element sealing portion (271, 371) and the light-receiving-element sealing portion (272, 372) each have a first surface disposed on the principal surface of the wiring board (260, 360), and the first surface of the light-emitting-element sealing portion (271, 371) abuts the light-emitting-element, and the first surface of the light-receiving-element sealing portion (272, 372) abuts the light-receiving-element; wherein an end portion of the cover (290, 390) closer to the light receiving element (223, 323) is disposed such that the end portion does not overlap the light-receiving-element sealing portion (272, 372) when viewed from a direction normal to the principal surface of the wiring board (260, 360), and/or wherein an end portion of the cover (290, 390) closer to the light emitting element (221, 222, 321, 322) is disposed such that the end portion does not overlap the light-emitting-element sealing portion (271, 371) when viewed from a direction normal to the principal surface of the wiring board (260, 360). a wiring board (260, 360); a light emitting element (221, 222, 321, 322) and a light receiving element (223, 323) 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 (271, 371) having light transmitting properties and configured to seal the light emitting element (221, 222, 321, 322); a light-receiving-element sealing portion (272, 372) having light transmitting properties and configured to seal the light receiving element (223, 323); a light shielding portion (273, 373) disposed between the light-emitting-element sealing portion (271, 371) and the light-receiving-element sealing portion (272, 372); and a cover (290, 390) having light transmitting properties, disposed in parallel with the wiring board (260, 360) with the light shielding portion (273, 373) therebetween, wherein the light-emitting-element sealing portion (271, 371) and the light-receiving-element sealing portion (272, 372) each have a first surface disposed on the principal surface of the wiring board (260, 360), and the first surface of the light-emitting-element sealing portion (271, 371) abuts the light-emitting-element, and the first surface of the light-receiving-element sealing portion (272, 372) abuts the light-receiving-element; wherein an end portion of the cover (290, 390) closer to the light receiving element (223, 323) is disposed such that the end portion does not overlap the light-receiving-element sealing portion (272, 372) when viewed from a direction normal to the principal surface of the wiring board (260, 360), and/or wherein an end portion of the cover (290, 390) closer to the light emitting element (221, 222, 321, 322) is disposed such that the end portion does not overlap the light-emitting-element sealing portion (271, 371) when viewed from a direction normal to the principal surface of the wiring board (260, 360).