Hydraulic oil storage device and injection molding device

A hydraulic oil storage device comprising:

• a main tank being connected with a suction tube that suctions hydraulic oil;
• a sub-tank being connected with a return tube that returns the hydraulic oil suctioned by the suction tube;
• and
• a coupling tube that connects the main tank and the sub-tank;
• wherein
• the sub-tank is provided with a partition portion that partitions a storage region of the sub-tank into a first region that includes a flow channel opening portion for the coupling tube, and a second region other than the first region;
• the partition portion is provided with an internal region communication portion that brings the first region and the second region into communication, and causes a pressure loss equal to or greater than the pressure loss of the coupling tube;
• and
• the return tube is connected to the sub-tank so that the flow channel outlet of the return tube faces the first region.