PURPOSE: To eliminate the need for maintenance and measure a wind speed acculately by providing a dust protecting member atop of transmitting and receiving elements which transmit and receive an ultrasonic pulse signal.

CONSTITUTION: Transmitting and receiving elements 1a and 1b for ultrasonic pulses are provided at a specific interval L and sends ultrasonic pulse signals 3a and 3b alternately and repeatedly at specific intervals of time. At this time, an ultrasonic wave propagation axis component is Vx=(L/2).(t1-t2/t1t2) (where t1 is the propagation time from the element 1a to the 1b and t2 is the propagation time from the element 1b to the 1a) and the wind speed V is calculated from Vx=V.cosθ (where θ is the angle between a wind direction and an axis of ultrasonic wave propagation). Then, the dust protecting member 4, e.g. dust propagating cylinder is provided atop of the transmitting and receiving elements 1a and 1b. Therefore, the dust protecting member prevents the elements from being stained, so the need for maintenance is eliminated and the wind speed is measured with high accuracy.