This invention provides a sensor-clamp device for clamping a pipe 4 of different outer-diameters promptly without having to do a time-consuming sensor-position adjustment. The sensor-clamp device 2 comprises a pair of ultrasonic-sensors 11, 12 incorporating an ultrasonic-transducer 10 for sending and receiving ultrasonic-waves ‘So’ and comprises a supporting-plate 30 on which is provided a sliding-mechanism 33. The pair of ultrasonic-sensors 11, 12 clamps the outer-wall 5 of the pipe 4 in which flows a fluid W1. Of the supporting-plate 30, the pair of ultrasonic-sensors 11, 12 used in irradiating the ultrasonic-waves ‘So’ obliquely to the pipe 4 are offset in the axial-line direction of said pipe 4 and firmly placed face to face. The sliding-mechanism 33 slides one of the pair of ultrasonic-sensors 11 obliquely with respect to the axial-line direction of the pipe 4, thus making the sliding-mechanism 33 to clamp the pipe 4 of various outer-diameters.
