A housing of a Roots pump is configured by joining a lower housing member and an upper housing member that are separable from each other. With the upper and lower housing members joined together, an upper accommodating portion and a lower accommodating portion form a front bearing accommodating portion and a rear bearing accommodating portion, which accommodate whole bearings, respectively. The Roots pump further includes bearing holders attached to the bearings and fixed to the lower housing member so that the bearings are received in the lower accommodating portion in a positioned state.