Ultrasonic sensor

An ultrasonic sensor, comprising:

• a plurality of first elements;
• and
• a plurality of second elements,
• the plurality of first elements emitting a first ultrasonic wave,
• a first operation being performed, the first operation including processing based on a first signal, the first signal corresponding to a first reflected wave of the first ultrasonic wave and being obtained from NR of the second elements (NR being an integer of 3 or more) included in the plurality of second elements,
• the plurality of first elements being arranged in a first direction at a first pitch pT, the first pitch pT being in the first direction,
• the NR second elements being arranged at a pitch of the plurality of second elements, a component in the first direction of the pitch of the plurality of second elements being a second pitch pR,
• NR, the first pitch pT, and the second pitch pR satisfying
• pR/pT=(NR+j)/NR (1), and
• j≠n·NR/m (2),
• m being an integer not less than 1 and not more than k,
• n being an integer not less than 1 and not more than (m− 1),
• j being an integer not less than 1 and not more than (NR−1),
• k being an integer not less than 2 and not more than 6.