To provide a space-saving unit with an improved noise cutoff characteristic, having an ultrasonic sensor using a piezoelectric element combined with a circuit for controlling transmission and reception of the ultrasonic wave and being featured by the ultrasonic sensor having a built-in variable transformer.

In the unit having the ultrasonic sensor including the piezoelectric element adhered to the internal bottom face of a bottomed cylindrical case formed of a metal or a resin including a metal component, the variable transformer is embedded inside the case configuring the ultrasonic sensor.