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