To measure a wave height and a shore-approaching speed by means of one apparatus, by a method wherein an are in which an ultrasonic sensor is attached at its tip is coupled to a support so as to be bendable.

A control part 9 which detects that an arm 2 is horizontal makes an ultrasonic sensor 3 transmit a high-frequency current. Ultrasonic waves T are transmitted toward the surface of he sea 5 from the ultrasonic sensor 3, reflected ultrasonic waves R are received by the ultrasonic sensor 3, the waves are inputted to the control part 9, and a wave height is measured. After a port entrance permission is reported to a ship 6, an arm 2 is turned by 90° from its present horizontal position to be vertical by an instruction signal from the control part 9. The control part 9 which detects the verticality of the arm 2 makes the ultrasonic sensor 3 transmit a high-frequency current. Ultrasonic waves T are transmitted to the ship 6 from the ultrasonic sensor 3, reflected ultrasonic waves R from the ship 6 are received by the ultrasonic sensor 3, and its electric signal is inputted to the control part 9. The control part 9 measures the shore-approaching speed of the ship 6 on the basis of a received signal.