PURPOSE: To protect a transmitter-receiver from the collision with a submerged obstacle under a state of enhancing searching accuracy, by mounting a cover part covering the front surface part of the transmitter-receiver at least in a propelling direction on the mount member of the transmitter-receiver.

CONSTITUTION: The mount member 26 extending forwardly from the front surface part of a propeller main body 11 is fixed by a bolt 26 and has a recessed part provided to the under surface of the leading end part thereof faced forwardly in a propelling direction and the transmitter-receiver 27 of a school-of-fish/depth-of-water searching apparatus is mounted to said recessed part by a clamp screw. A cover part 26C is provided so as to cover the entire outer peripheral part containing the front surface part of the transmitter-receiver 27 in the propelling direction. By this constitution, a submerged obstacle such as drift wood colliding with the cover part 26C of the mount member 26 flows away behind the propeller main body 11 and the transmitter-receiver 27 can be protected from the collision with the submerged obstacle.