PURPOSE: To make working oil flow to the oil chamber regardless of restrictions due to the layout of inlet and outlet ports.

CONSTITUTION: This reservoir tank is a reservoir body 1 in which a first oil chamber 4a, etc., for storing working oil in it and a first inlet and outlet ports communicated with the first oil chamber 4a, etc. This reservoir body 1 is composed of a second oil chamber 10 formed by dividing the first oil chamber 4a, etc., by means of vertical partitions, a second inlet port 9a and a second outlet port 9b which are formed in the reservoir body 1 and communicated with the second oil chamber 10, an upper chamber 10a and a lower chamber 10b formed by dividing the second oil chamber 10 by means of a horizontal partition wall 5b, a partition wall 11a formed on the horizontal partition wail 5b at the part near to the second inlet port 9a, and a foreign object removing net part 11 formed at the part near to the second outlet port 9b.