Multistage vacuum pump

A multistage vacuum pump in which a plurality of pump chambers are formed by a housing and a partition plate, the plurality of pump chambers are connected via a gas passage formed in the partition plate, a pair of rotors attached to a shaft are disposed in each of the pump chambers, and when the pair of rotors rotate while intermeshing, a suctioned gas is compressed and then discharged through a discharge side recessed portion that communicates with the gas passage,

• the multistage vacuum pump being characterized in that
• angles of the rotors relative to the shaft are adjusted such that a phase angle Δθ of the rotors of adjacent pump chambers relative to a rotation angle C of the rotors during a single cycle of the pump chambers from intake to discharge and the number of stages S of the rotors satisfies Δθ≦C/S, and when a rotor angle φ from a reference position to an opening start point of the discharge side recessed portion is set as a first stage rotor angle φ1, an mth stage rotor angle φm, and an nth stage rotor angle φn in order from an upstream side of a gas flow direction, relationships of φ1≦φm≦n and φ1<φn (where n and m are natural numbers and n>m) are satisfied.