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 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 ; a second cooling pipe connected to the second pipe joint and to a downstream portion of the cooler ; a power conversion controller , wherein the cooler is a bi-directional cooler sandwiched between the generator and the power conversion controller , and configured to cool both the generator and the power conversion controller using the fluid flowing through the cooling pipe , the power conversion controller 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 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 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 ; a second cooling pipe connected to the second pipe joint and to a downstream portion of the cooler ; a power conversion controller , wherein the cooler is a bi-directional cooler sandwiched between the generator and the power conversion controller , and configured to cool both the generator and the power conversion controller using the fluid flowing through the cooling pipe , the power conversion controller 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 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 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 . <EOS>