A passage block coupling apparatus including a bolt insertion hole 13 and a pin insertion hole 14 formed in an upper-stage passage block 3, a screw hole 15 and a non-screw hole 16 that are formed in a lower-stage passage block 4, a bolt 11 that is inserted into the bolt insertion hole 13, and threaded with the screw hole 15, and a positioning pin 12 that is inserted to the pin insertion hole 14, with its lower end portion being fitted to the non-screw hole 16. A cut-out section 17 is formed near the lower end portion of the positioning pin 12, and a protruding portion 18 to be fitted to the cut-out section 17 is formed on the opening portion of the non-screw hole 16. A tightening force exerted by the bolt 11 and a force exerted by the lower end portion of the positioning pin 12 to press the protruding portion 18 of the non-screw hole 16 upward are balanced with each other so that an evenly fastened state is achieved so that the passage blocks 3 and 4 are coupled with each other.