The first member and the second member include, when a line that connects a first port and a second port is denoted by a reference line, a first groove that has a central point on the reference line and extends in a direction that intersects with the reference line; a second groove that connects one end of the first groove and the first port; a third groove that connects the other end of the first groove and the first port and has a shape that is line symmetrical to the second groove with respect to the reference line; a fourth groove that connects the other end (FN2) of the first groove and the second port; and a fifth groove that connects one end (FN1) of the first groove and the second port and has a shape that is line symmetrical to the fourth groove with respect to the reference line.