An underwater detection apparatus , comprising: a transmission transducer configured to transmit a transmission wave within a given transmission fan-shaped space (T1, T2, T1E), the transmission fan-shaped space (T1, T2, T1E) having a first transmission width (Tθ1, Tθ3) in a given first plane (P1) and a second transmission width (Tθ2, Tθ4) in a second plane (P2) perpendicular to the first plane (P1); a reception transducer configured to receive a reflection wave of the transmission wave within a given reception fan-shaped space (R1, R2, R1E), the reception fan-shaped space (R1, R2, R1E) having a first reception width (Rθ1, Rθ3) in the first plane (P1) and a second reception width (Rθ2, Rθ4) in the second plane (P2), the second reception width (Rθ2, Rθ4) being narrower than the second transmission width (Tθ2, Tθ4); and in the second plane (P2), one of a pair of edges of the transmission fan shaped space (T1, T2, T1E) being within the reception fan shaped space (R1, R2, R1E); a motor configured to rotate the transmission fan-shaped space (T1, T2, T1E) and the reception fan-shaped space (R1, R2, R1E); and a controller configured to control the motor ; characterized in that : the controller controls the motor to rotate at a given first speed (V1) when the transmission transducer and the reception transducer perform an underwater detection, and at a second speed (V2) faster than the first speed (V1) when the underwater detection is not performed; wherein the controller controls the motor to rotate in a given first direction in both cases when the underwater detection is performed and when the underwater detection is not performed. a transmission transducer configured to transmit a transmission wave within a given transmission fan-shaped space (T1, T2, T1E), the transmission fan-shaped space (T1, T2, T1E) having a first transmission width (Tθ1, Tθ3) in a given first plane (P1) and a second transmission width (Tθ2, Tθ4) in a second plane (P2) perpendicular to the first plane (P1); a reception transducer configured to receive a reflection wave of the transmission wave within a given reception fan-shaped space (R1, R2, R1E), the reception fan-shaped space (R1, R2, R1E) having a first reception width (Rθ1, Rθ3) in the first plane (P1) and a second reception width (Rθ2, Rθ4) in the second plane (P2), the second reception width (Rθ2, Rθ4) being narrower than the second transmission width (Tθ2, Tθ4); and in the second plane (P2), one of a pair of edges of the transmission fan shaped space (T1, T2, T1E) being within the reception fan shaped space (R1, R2, R1E); a motor configured to rotate the transmission fan-shaped space (T1, T2, T1E) and the reception fan-shaped space (R1, R2, R1E); and a controller configured to control the motor ; characterized in that : the controller controls the motor to rotate at a given first speed (V1) when the transmission transducer and the reception transducer perform an underwater detection, and at a second speed (V2) faster than the first speed (V1) when the underwater detection is not performed; wherein the controller controls the motor to rotate in a given first direction in both cases when the underwater detection is performed and when the underwater detection is not performed. the controller controls the motor to rotate at a given first speed (V1) when the transmission transducer and the reception transducer perform an underwater detection, and at a second speed (V2) faster than the first speed (V1) when the underwater detection is not performed; wherein the controller controls the motor to rotate in a given first direction in both cases when the underwater detection is performed and when the underwater detection is not performed. <EOS>