It has been reported that an object can be suspended below a vibrating surface in air. We call this phenomenon ultrasonic suspension. When an object is suspended, a restoring force attracts the object horizontally to the center of the vibrating surface. Previously, characteristics of the forces acting vertically and horizontally were experimentally investigated using a servo-type measuring mechanism. While ultrasonic vibration was being excited, actuation forces acting on the object were measured. This characterization implied that negative pressure is generated in the suspension gap. To determine the principles governing these forces, the pressure distribution in the gap was investigated. Two types of pressure sensors were prepared. Measurements by these sensors did not agree with the characterized force, because a small hole at the measuring point in both sensors influenced the results. Therefore, we proposed a novel pressure sensor employing a diaphragm. Deflection of the diaphragm in proportion to applied pressure can be expected. The sensor was prototyped by micro-electromechanical system (MEMS) technology and calibrated. Results show that the deflection was proportional to the applied pressure and had no hysteresis.