A vacuum pump comprising: a pump casing including a plurality of pump chambers (50a-50f) held in fluid communication with each other and arrayed in a longitudinal direction thereof, an inlet port held in fluid communication with one of the pump chambers (50a-50f) which is positioned on a suction side, and an outlet port held in fluid communication with another one of the pump chambers (50a-50f) which is positioned on a discharge side; a rotational shaft rotatably supported at opposite ends thereof by bearings (86a, 86b) and extending in the longitudinal direction of the pump casing; and a plurality of rotors (60a-60f) housed in the pump chambers (50a-50f) and coupled to the rotational shaft for rotation in unison with the rotational shaft; wherein the pump casing includes: an intermediate chamber disposed adjacent to and outside of the one of the pump chambers (50a-50f) which is held in fluid communication with the outlet port, and held in fluid communication with this one of the pump chambers (50a-50f); an end wall located between the intermediate chamber and the one of the pump chambers (50a-50f), the end wall having a discharge hole and a reverse flow hole; the vacuum pump being characterised by a partition for preventing a process gas, discharged from the discharge hole from directly flowing into the reverse-flow hole. a pump casing including a plurality of pump chambers (50a-50f) held in fluid communication with each other and arrayed in a longitudinal direction thereof, an inlet port held in fluid communication with one of the pump chambers (50a-50f) which is positioned on a suction side, and an outlet port held in fluid communication with another one of the pump chambers (50a-50f) which is positioned on a discharge side; a rotational shaft rotatably supported at opposite ends thereof by bearings (86a, 86b) and extending in the longitudinal direction of the pump casing; and a plurality of rotors (60a-60f) housed in the pump chambers (50a-50f) and coupled to the rotational shaft for rotation in unison with the rotational shaft; wherein the pump casing includes: an intermediate chamber disposed adjacent to and outside of the one of the pump chambers (50a-50f) which is held in fluid communication with the outlet port, and held in fluid communication with this one of the pump chambers (50a-50f); an end wall located between the intermediate chamber and the one of the pump chambers (50a-50f), the end wall having a discharge hole and a reverse flow hole; the vacuum pump being characterised by a partition for preventing a process gas, discharged from the discharge hole from directly flowing into the reverse-flow hole. an intermediate chamber disposed adjacent to and outside of the one of the pump chambers (50a-50f) which is held in fluid communication with the outlet port, and held in fluid communication with this one of the pump chambers (50a-50f); an end wall located between the intermediate chamber and the one of the pump chambers (50a-50f), the end wall having a discharge hole and a reverse flow hole; the vacuum pump being characterised by a partition for preventing a process gas, discharged from the discharge hole from directly flowing into the reverse-flow hole.