part 19 a of a pin plug 19 into one of the radial holes 7 a u02dc 7 d assuming that internal volume ratio can be set for example to 2 3 2 63 3 65 and 5 0 in the case of fig1 the state in fig1 in which the pin part 19 a of the pin plug 19 screwed into the screw hole 20 is inserted into the radial hole 7 a is the state that internal volume ratio is set to 2 3 if the internal volume ratio adjusting slide valve 7 is moved to the left and the pin part 19 a of the pin plug 19 is inserted into the radial hole 7 b internal volume ratio is increased to 2 63 then when the blank plug 21 is removed and the pin plug 19 is screwed into the screw hole 22 in the rotor casing 1 if the pin part 19 a is inserted into the radial hole 7 c internal volume ratio is increased to 3 65 and if the pin part 19 a is inserted into the radial hole 7 d internal volume ratio is increased to 5 0 when the rotation handle 17 is rotated to slide the capacity adjusting valve 5 to the left in the state the internal volume ratio adjusting slide valve 7 is secured in place the capacity adjusting slide valve moves.