Sonar unit

A sonar unit comprising:

• a transducer configured to receive an ultrasonic wave;
• a rectangular circuit substrate on which the transducer, electronic components constituting a circuit configured to drive the transducer, and an input-output terminal for the circuit are mounted, the transducer comprising a body housing a piezoelectric element on a first side of the rectangular circuit substrate;
• and
• a shield unit placed in the rectangular circuit substrate, the shield unit being configured to block an electromagnetic wave incident on the electronic components, wherein:
• the input-output terminal is placed on a first end side of the rectangular circuit substrate in a longitudinal direction of the rectangular circuit substrate;
• the shield unit includes a plate portion at a position where the plate portion overlaps at least a part of the electronic components when the shield unit is viewed in a thickness direction of the rectangular circuit substrate, the plate portion of the shield unit being on a second side of the rectangular circuit substrate opposite the first side;
• the shield unit includes a window portion provided as a through-hole or a notch penetrating through the plate portion in a thickness direction of the plate portion;
• and
• the window portion is placed at a position close to the input-output terminal in the longitudinal direction of the rectangular circuit substrate, without overlapping the input-output terminal, when the window portion is viewed in the thickness direction of the rectangular circuit substrate.