An ultrasonic transducer element chip characterized by comprising a substrate including openings arranged in an array pattern, ultrasonic transducer elements respectively disposed at the openings on a first surface of the substrate, and a reinforcing member fixed on a second surface of the substrate opposite to the first surface of the substrate to reinforce the substrate, the reinforcing member including linear groove parts formed on a surface of the reinforcing member fixed on the second surface of the substrate so that internal spaces of the openings and an external space of the substrate are in communication with each other via the linear groove parts, the linear groove parts extending along a plane of the surface of the reinforcing member, and the linear groove parts being arranged at an interval in a first direction smaller than a width of each of the openings on the second surface of the substrate in the first direction.
