PURPOSE: To easily introduce washing liquid such as solvent into a pair of shaft seal parts and the rear surface part of an internally rotating gear located in a liquid feed passage for handling viscous fluid, that is, outside of a drive shaft.

CONSTITUTION: A liquid flowing hole 15 extended from the pump chamber (p) side to a position around a mechanical seal located outside a drive shaft 2 is formed in a drive shaft 2 fixed to an internally rotating gear 1a and vertically extended. Further, a small hole 17 extending the end face on the pump chamber (p) side to the end face remote therefrom is formed in the rear plate 16 part of the internally rotating gear 1a. The end face of the internally rotating gear 1a on the mechanical seal 8, 9 side is coated thereover with a flouroresin coating 18. Further, the inner surface of a casing 3 on the mechanical seal 8, 9 side is coated thereover with a fluororesin coating 19.