A biological testing device includes a main unit including an ultrasonic wave transmitting/receiving part, and an attaching member for attaching the main unit on a tested object. The ultrasonic wave transmitting/receiving part includes a sensor array substrate including ultrasonic transducers, first and second resin material parts, and an ultrasonic wave transmitting medium. The first resin material part forms a first space closed off from an outside space between the first resin material part and the sensor array substrate with the first resin material part facing the ultrasonic transducers. The second resin material part forms a second space communicating with the first space. The second space is closed off from the outside space, at least a portion of the second resin material part including a flexible portion configured and arranged to bulge toward the outside space. The ultrasonic wave transmitting medium fills the first space and the second space.
