To provide an operating oil tank 4 for a work machine which is arranged in an upper rotary body 3 rotatably mounted on a lower traveling body 2, wherein the operating oil tank 4 need not have a special washing hole formed therein in a process of manufacturing the operating oil tank 4, and for use specifically in washing the interior of the tank by inserting a washing nozzle.

The operating oil tank 4 has formed therein a first suction port 6 for sucking operating oil fed to hydraulic equipment as a standard component, and a second suction port 7 for sucking operating oil fed to hydraulic equipment other than the standard component, and the second suction port 7 doubles as the washing hole, to thereby dispense with the special washing hole. Further the operating oil tank 4 which has the second suction port 7 covered with a cover body 10 is manufactured as a generally applicable tank model. Therefore if a pressure oil feeding pipe is necessary for retrofitted hydraulic equipment, the cover body 10 is removed and the second suction port 7 is connected to the pipe 11 via a joint member 12, to thereby manufacture an operating oil tank 4 of a special specification.