PURPOSE: To avoid the need of cleaning an inflow side strainer by installing a strainer which is demounted after the oil feeding test at a site, onto the inside of the inflow side strainer.

CONSTITUTION: An inflow side strainer 20 of a pump device U consists of a brass net 20c laid between an installation metal fitting 20a and a pressing metal fitting 20b. On the inner periphery of the inflow side strainer 20, a throw-away strainer 22 is installed so as to be closely fitted onto the inner periphery. Though, when the oil feeding test is carried out, dusts adhere onto the inner periphery of the throw-away strainer 22, the throw-away strainer 22 is pulled out from the inflow side strainer 20. Therefore, the need of cleaning the inflow side strainer 20 can be avoided.