A fluid device including a hydropower machine and a generator coupled to the hydropower machine, the hydropower machine and the generator being detachably coupled to each other, the fluid device comprising: a first pipe joint connected to an inlet pipe of the hydropower machine and configured to introduce a fluid to the hydropower machine, the first pipe joint being separated from the hydropower machine; a second pipe joint connected to an outlet pipe of the hydropower machine and configured to lead the fluid out of the hydropower machine, the second pipe joint being separated from the hydropower machine; a cooler (30, 31) configured to carry out liquid-cooling using the fluid; a first cooling pipe connected to the first pipe joint and to an upstream portion of the cooler (30, 31); a second cooling pipe connected to the second pipe joint and to a downstream portion of the cooler (30, 31); a power conversion controller (20, 21), wherein the cooler (30, 31) is a bi-directional cooler (30, 31) sandwiched between the generator and the power conversion controller (20, 21), and configured to cool both the generator and the power conversion controller (20, 21) using the fluid flowing through the cooling pipe (40, 41), the power conversion controller (20, 21) includes: a first power conversion controller configured to convert or control power obtained by the generator or from a power source; and a second power conversion controller configured to further convert or control the power converted or controlled by the first power conversion controller, and the bi-directional cooler (30, 31) includes: a first cooler sandwiched between the generator and the first power conversion controller; and a second cooler sandwiched between the generator and the second power conversion controller. a first pipe joint connected to an inlet pipe of the hydropower machine and configured to introduce a fluid to the hydropower machine, the first pipe joint being separated from the hydropower machine; a second pipe joint connected to an outlet pipe of the hydropower machine and configured to lead the fluid out of the hydropower machine, the second pipe joint being separated from the hydropower machine; a cooler (30, 31) configured to carry out liquid-cooling using the fluid; a first cooling pipe connected to the first pipe joint and to an upstream portion of the cooler (30, 31); a second cooling pipe connected to the second pipe joint and to a downstream portion of the cooler (30, 31); a power conversion controller (20, 21), wherein the cooler (30, 31) is a bi-directional cooler (30, 31) sandwiched between the generator and the power conversion controller (20, 21), and configured to cool both the generator and the power conversion controller (20, 21) using the fluid flowing through the cooling pipe (40, 41), the power conversion controller (20, 21) includes: a first power conversion controller configured to convert or control power obtained by the generator or from a power source; and a second power conversion controller configured to further convert or control the power converted or controlled by the first power conversion controller, and the bi-directional cooler (30, 31) includes: a first cooler sandwiched between the generator and the first power conversion controller; and a second cooler sandwiched between the generator and the second power conversion controller. a first power conversion controller configured to convert or control power obtained by the generator or from a power source; and a second power conversion controller configured to further convert or control the power converted or controlled by the first power conversion controller, and the bi-directional cooler (30, 31) includes: a first cooler sandwiched between the generator and the first power conversion controller; and a second cooler sandwiched between the generator and the second power conversion controller. a first cooler sandwiched between the generator and the first power conversion controller; and a second cooler sandwiched between the generator and the second power conversion controller.