An ultrasonic transducer and a focused ultrasound treatment device, relating to the technical field of high intensity focused ultrasound and capable of solving the problem that an existing ultrasonic transducer has a large focal zone and is in the shape of a "cigar". The ultrasonic transducer comprises a sound producing unit and a sound producing surface (3)； the sound producing unit is used for producing ultrasonic waves； the sound producing surface (3) is a spherical surface having a first notch (31), a second notch (32), and a third notch (33)； a sphere center surface of the spherical surface corresponding to the sound producing surface (3) is a main sphere center surface (99)； the first notch (31) and the second notch (32) are respectively located at two positions where a diameter perpendicular to the main sphere center surface (99) intersects with the spherical surface； the third notch (33) is connected to the first notch (31) and the second notch (32)； within a range separately spacing from two sides of the main sphere center surface (99) by a certain distance, the sound producing surface (3) is a circular arc in a cross section parallel to the main sphere center surface (99)； an opening of the circular arc corresponds to the third notch (33)； the central angle of the circular arc is greater than 180 degrees and smaller than 360 degrees； the sound producing surface (3) can reflect ultrasound and the ultrasonic waves produced by the sound producing unit are focused at a sphere center corresponding to the sound producing surface (3).
