To make the direction of a detecting part freely changeable in addition to the directions of a transmission part and a meter, in response to the condition in an installed field.

A pair of pressure introducing covers 12 for holding both sides of the detecting part 10 is fixed to a cover attaching part 8 provided on an upper face of a pipe body 4 by four bolts 9. Threaded hole screwed in with the bolts 9 has equal pitches P1, P2 ( P1=P2 ) between the vertical and lateral fellow adjacent holes, formed into square array, and constituted to make the directions of the detecting part 10 and the covers 12 changeable in angle in every 90° within a horizontal plane. The transmission part 11 is attached rotatably to a cylindrical body 40 for connection provided in the detecting part 10. The detecting part 10 is changeable in angle within a vertical plane with respect to the covers 12, and can change the direction of the transmission part 11 in three-way manner of frontward, upward and rearward direction.