This ultrasonic transducer element chip is characterized by being provided with: a substrate having openings arranged in an array ultrasonic transducer elements disposed at each of the openings on a first surface of the substrate a reinforcing member that is fixed to a second surface of the substrate which is on the opposite side of the first surface of the substrate and reinforces the substrate and ventilation channels by which the internal space of the openings and the external space of the substrate communicate with each other.