<p>A connecting member (5A) is provided with a hollow shaft (51) with both ends fitted inside a central tube (21) of a spiral separation membrane element (2), and a plate (52) that extends to the periphery from the central section of the shaft (51). At least one of the shaft (51) and the plate (52) has sensors attached thereon, and an antenna (65) connected to the sensors is arranged on the plate (52). The length (L) of protrusion of both ends of the shaft (51) from the plate (52) is 0.2-1.4 times the outer diameter of the shaft (51).</p>
