<p>A plug section (27) is projected from a first block (1) so as to be insertable into an insertion hole (5) in a second block (2). A supporting surface (9a) is provided on the first block (1) so as to be able to contact with a to-be-supported surface (2a) of the second block (2). A fluid circulation hole (59) is formed in the supporting surface (9a). A gap-maintaining member (K) is provided in the first block (1). The gap- maintaining member (K) causes a force to act on the second block (2) in the direction to separate the second block (2) from the first block (1) to form a gap (G1) between the to-be-supported surface (2a) and the supporting surface (9a). A tension member (21) makes the second block (2) approach the first block (1) against an action force of the gap-maintaining member (K) with the outer peripheral surface of the plug section (27) in tight contact with the inner peripheral surface of the insertion hole (5), eliminating the gap (G1) to cause the supporting surface (9a) and the to-be-supported surface (2a) to be in contact with each other.</p>
