To reduce the size of a pump housing without lowering the performance of a pump, to implement a high degree of freedom in installing or mounting the pump in a limited space, to share a housing main body, and to easily adopt the various kinds of the partition wall members.

This magnet pump is constituted of the housing body A and the partition wall member B. The housing main body A comprises: a perfectly circular inner peripheral wall face 1, a side face portion 2; a spiral wall face 3 formed inward to be extended downward in a step-like manner; a vertical wall portion 4 having a spiral circular arc face 4a formed inward the continuous to the spiral wall face 3 and a perfect-arc-shaped face 4b formed on an outer peripheral side to be spaced from the inner peripheral wall face 1 and have the same center of the inner peripheral wall face 1. The partition wall member B has a perfectly cylindrical connecting portion 11 inserted water-tightly into the inner peripheral wall face 1.