A pump wherein a discharge port for discharging a working fluid in the vicinity of a mechanical seal to the outside of a casing is provided so as to be communicated to the portion of the outer circumferential surface of a rotary shaft between an impeller and the mechanical seal. The mechanical seal is fitted in the outer circumferential surface of the rotary shaft and adapted to seal the rotary shaft against the working fluid flowing from a fluid passage to the outer circumferential surface of the rotary shaft. The vane of the impeller is provided with a plurality of radially extending blades and recesses among the blades, the blades and the bottom portions of the recesses in the vane being joined together by curved surfaces.
