A housing (2) of a Roots pump (1) supports a drive shaft (3) and a driven shaft (4) with radial bearings (32, 33) so as to be rotatable. The housing (2) is formed by joining an upper housing member (20) to a lower housing member (10). The lower housing member (10) has lower bearing support portions (13), and the upper housing member (20) has upper bearing support portions (23). Opening edges (13a) of each lower bearing support portion (13) are positioned above the centers (P1) of the bearings (32, 33). An opening width (T1) of each lower bearing support portion (13) is smaller than the diameter (D1) of the bearings (32, 33). This structure suppresses the bearings (32, 33) from being separated from the lower housing member (10) during an assembling operation of the fluid machine.