PURPOSE: To reduce the mental burden upon a helmsman, by using the difference in the pitch of a sound or the period of an intermittent sound in addition to visual indication to inform the turning direction and its velocity of ship.

CONSTITUTION: A ship's turning angle transmitted from a gyroscope 1 is applied to a signal converter 2 so that the angle is changed into a digital signal. This digital signal is applied to a calculator 3 to compute the angular velocity and pick out the rotating direction of the ship and the magnitude of the angular velocity in the form of digital codes.These digital codes are applied to a display section according to an instruction so tht the codes are indicated and entered into a low frequency generation unit 5. This unit produces a low-frequency intermittent output signal which has low frequency showing the turning direction of the ship and an intermission period showing the magnitude of the angular velocity of turning. The output signal drives a sound generator 6. The pitch of a sound is changed depending on the turning direction. The period of an intermittent sound is altered depending on the magnitude of the angular velocity of the turning. Since a helmsman can obtain information of the ship's turning from the sound while watching forward, the mental burden upon the helmsman can be reduced.