A biological information detecting device or the like in which waterproof performance or the like is improved by a simple structure is provided. A biological information detecting device includes a sensor unit 130 which detects biological information of a test body, and a case portion 300 in which the sensor unit 130 is disposed. The case portion 300 is provided with a light transmitting portion 30 including a detection window 120 which transmits light incident on the sensor unit 130, and a light blocking portion 20 blocking light from being incident on an inner portion of the case portion 300. In a case where a direction towards the sensor unit 130 from the test body at the time of mounting the biological information detecting device is set to a first direction DR1, a joining portion 52 between the light transmitting portion 30 and the light blocking portion 20 protrudes or is dented along a direction intersecting with the first direction DR1.
