To reduce a skew amount and improve productivity, by determining a least common multiple of the number of fixed blades and the number of moving blades and a radius from a rotational center line to a gap position formed between a fixed blade and a moving blade, and by representing the skew amount of fixed blades or moving blades with a specific expression.

Fixed blades 7 and rotational moving blades 9 are respectively placed in a housing of a pump, the number of the fixed blades 7 is set to 3, 6, 12,..., and the number of the moving blades 9 is set to 4, 8, 16,.... Because the number of the fixed blades 7 is 6 and the number of the moving blades 9 is 8 here, their least common multiple is 24, and a given skew amount S is provided to the fixed blades 7 based on the cycle of variable force generated at this time. The skew amount S is derived by 2 π R/L, where R is a radius from a rotational center line X to a gap position formed between the fixed blade 7 and the moving blade 9, and L is a least common multiple of each number of blades. Thus, the skew amount S can be set small, and the entire noise and vibration can be restrained small.