An ultrasonic sensor comprising: a fixed frame fixed to an external member; an ultrasonic oscillator disposed inside the fixed frame, the ultrasonic oscillator comprising a flexible first substrate (3 A) and a first piezoelectric element (3B, 3C, 3D) deposited on the first substrate (3 A) in a form of a thin film, the ultrasonic oscillator being configured to be warped in response to expansion or contraction of the first piezoelectric element (3B, 3C, 3D) and generate ultrasonic waves; and at least two actuator units arranged symmetrically around the flexible first substrate, comprising a flexible second substrate and each comprising a second piezoelectric element (4B, 4C, 4D) deposited on the second substrate in a form of a thin film, the actuator units being configured to in response to expansion or contraction of the second piezoelectric element (4B, 4C, 4D) cause the ultrasonic oscillator to swing relative to the fixed frame, wherein the first substrate (3 A) has an outer periphery part bonded to the actuator units and an inner periphery part provided with the first piezoelectric element (3B, 3C, 3D), the inner periphery part having a thickness smaller than the outer periphery part so as to be warped in response to expansion or contraction of the first piezoelectric element (3B, 3C, 3D) and generate ultrasonic waves, the second substrate includes: a first portion on which the second piezoelectric element (4B, 4C, 4D) is provided, the first portion being thinner than the outer periphery part of the first substrate (3 A) and being warped in response to expansion of the second piezoelectric element (4B, 4C, 4D) to cause the ultrasonic oscillator to swing; and a second portion connecting the first portion to the outer periphery part, the second portion having a thickness same as a thickness of the first portion, the first substrate being coupled to the fixed frame only through the actuator units. a fixed frame fixed to an external member; an ultrasonic oscillator disposed inside the fixed frame, the ultrasonic oscillator comprising a flexible first substrate (3 A) and a first piezoelectric element (3B, 3C, 3D) deposited on the first substrate (3 A) in a form of a thin film, the ultrasonic oscillator being configured to be warped in response to expansion or contraction of the first piezoelectric element (3B, 3C, 3D) and generate ultrasonic waves; and at least two actuator units arranged symmetrically around the flexible first substrate, comprising a flexible second substrate and each comprising a second piezoelectric element (4B, 4C, 4D) deposited on the second substrate in a form of a thin film, the actuator units being configured to in response to expansion or contraction of the second piezoelectric element (4B, 4C, 4D) cause the ultrasonic oscillator to swing relative to the fixed frame, wherein the first substrate (3 A) has an outer periphery part bonded to the actuator units and an inner periphery part provided with the first piezoelectric element (3B, 3C, 3D), the inner periphery part having a thickness smaller than the outer periphery part so as to be warped in response to expansion or contraction of the first piezoelectric element (3B, 3C, 3D) and generate ultrasonic waves, the second substrate includes: a first portion on which the second piezoelectric element (4B, 4C, 4D) is provided, the first portion being thinner than the outer periphery part of the first substrate (3 A) and being warped in response to expansion of the second piezoelectric element (4B, 4C, 4D) to cause the ultrasonic oscillator to swing; and