A transformer device comprising: - an iron core; - a plurality of coils (8A, 8B, 9A, 9B, 10A, 10B) wound onto the iron core and stacked with each other; - a plurality of base members arranged between the plurality of coils (8A, 8B, 9A, 9B, 10A, 10B) adjacent in a stacking direction; - a plurality of flow channel member groups provided for the plurality of base members, respectively, and each flow channel member group being provided at a corresponding base member for forming a flow channel for directing a flow of an insulating fluid between a corresponding base member and a corresponding coil (8A, 8B, 9A, 9B, 10A, 10B); wherein the channel flow member group includes: - a first array comprising a plurality of first flow channel members of a rectangular shape, provided extensively at an inlet side and outlet side region of the flow channels, said region being bounded by outermost first flow channel members of the plurality of first flow channel members, each first flow channel member having two long sides along the flowing direction of the insulating fluid, and two shorter sides substantially perpendicular to the flowing direction of the insulating fluid, and - a second array comprising a plurality of second flow channel members of a rectangular shape, provided extensively between the inlet side region and outlet side region of the flow channels, each having two long sides substantially perpendicular to the flowing direction of the insulating fluid and two shorter sides along the flowing direction of the insulating fluid, and - an obstruction member (12, 22, 32, 42) provided at at least one of the inlet side region or outlet side region of the flow channels, and having a portion in a direction substantially perpendicular to the flowing direction of the insulating fluid longer than a length of the two shorter sides of the first flow channel member, characterized in that: the obstruction member (12, 22, 32, 42) is arranged either within the first array of first flow channel members or arranged between said outermost first flow channel members as seen in the direction of the flow of the insulating fluid, and the obstruction member being arranged at the edge of the base member at the inlet side region of the base member to obstruct the flow of the insulating fluid such that at least one of the flow channels formed by the plurality of flow channel member groups differs in a flow volume of the insulating fluid from another of the flow channels, and to obstruct the flow of the insulating fluid at a region not overlapping with the iron core in a flowing direction of the insulating fluid among regions of the at least one of the flow channels, - an iron core; - a plurality of coils (8A, 8B, 9A, 9B, 10A, 10B) wound onto the iron core and stacked with each other; - a plurality of base members arranged between the plurality of coils (8A, 8B, 9A, 9B, 10A, 10B) adjacent in a stacking direction; - a plurality of flow channel member groups provided for the plurality of base members, respectively, and each flow channel member group being provided at a corresponding base member for forming a flow channel for directing a flow of an insulating fluid between a corresponding base member and a corresponding coil (8A, 8B, 9A, 9B, 10A, 10B); - a first array comprising a plurality of first flow channel members of a rectangular shape, provided extensively at an inlet side and outlet side region of the flow channels, said region being bounded by outermost first flow channel members of the plurality of first flow channel members, each first flow channel member having two long sides along the flowing direction of the insulating fluid, and two shorter sides substantially perpendicular to the flowing direction of the insulating fluid, and - a second array comprising a plurality of second flow channel members of a rectangular shape, provided extensively between the inlet side region and outlet side region of the flow channels, each having two long sides substantially perpendicular to the flowing direction of the insulating fluid and two shorter sides along the flowing direction of the insulating fluid, and - an obstruction member (12, 22, 32, 42) provided at at least one of the inlet side region or outlet side region of the flow channels, and having a portion in a direction substantially perpendicular to the flowing direction of the insulating fluid longer than a length of the two shorter sides of the first flow channel member, the obstruction member (12, 22, 32, 42) is arranged either within the first array of first flow channel members or arranged between said outermost first flow channel members as seen in the direction of the flow of the insulating fluid, and the obstruction member being arranged at the edge of the base member at the inlet side region of the base member to obstruct the flow of the insulating fluid such that at least one of the flow channels formed by the plurality of flow channel member groups differs in a flow volume of the insulating fluid from another of the flow channels, and to obstruct the flow of the insulating fluid at a region not overlapping with the iron core in a flowing direction of the insulating fluid among regions of the at least one of the flow channels,