A balloon-type electrode catheter for performing a high frequency ablation treatment, the balloon-type electrode catheter comprising: an outer tube that has a center lumen and a plurality of sub lumens that are disposed around the center lumen; an energization connector that is disposed on a proximal end side of the outer tube; a balloon that has an expansion portion that expands and contracts and a proximal-end-side neck portion and a distal-end-side neck portion that are continuous with both ends thereof, the balloon being connected to a distal end side of the outer tube as a result of the proximal-end-side neck portion being fixed to a distal end portion of the outer tube and the expansion portion containing the distal end portion of the outer tube; an inner shaft that is inserted into the center lumen of the outer tube, the inner shaft extending out through an opening of the center lumen into an inner portion of the balloon, being fixed to the distal-end-side neck portion of the balloon, and extending out to an outside of the balloon; a surface electrode that is formed by a metal thin film that is formed on an outer surface of the balloon at at least the expansion portion of the balloon; and a conducting wire that electrically connects the surface electrode and the energization connector to each other, wherein at least one of the sub lumens of the outer tube is a fluid supply sub lumen in which a fluid is caused to flow to supply the fluid into the inner portion of the balloon, wherein at least one of the sub lumens of the outer tube is a fluid drainage sub lumen in which the fluid is caused to flow to drain the fluid supplied into the inner portion of the balloon, from the inner portion of the balloon, wherein an opening of either one of the fluid supply sub lumen and the fluid drainage sub lumen is located on the distal end side from an intermediate location in an axial direction in the expansion portion, and wherein an opening of the other of the fluid supply sub lumen and the fluid drainage sub lumen is located at a proximal end of the expansion portion or in a vicinity thereof. an outer tube that has a center lumen and a plurality of sub lumens that are disposed around the center lumen; an energization connector that is disposed on a proximal end side of the outer tube; a balloon that has an expansion portion that expands and contracts and a proximal-end-side neck portion and a distal-end-side neck portion that are continuous with both ends thereof, the balloon being connected to a distal end side of the outer tube as a result of the proximal-end-side neck portion being fixed to a distal end portion of the outer tube and the expansion portion containing the distal end portion of the outer tube; an inner shaft that is inserted into the center lumen of the outer tube, the inner shaft extending out through an opening of the center lumen into an inner portion of the balloon, being fixed to the distal-end-side neck portion of the balloon, and extending out to an outside of the balloon; a surface electrode that is formed by a metal thin film that is formed on an outer surface of the balloon at at least the expansion portion of the balloon; and a conducting wire that electrically connects the surface electrode and the energization connector to each other, wherein at least one of the sub lumens of the outer tube is a fluid supply sub lumen in which a fluid is caused to flow to supply the fluid into the inner portion of the balloon, wherein at least one of the sub lumens of the outer tube is a fluid drainage sub lumen in which the fluid is caused to flow to drain the fluid supplied into the inner portion of the balloon, from the inner portion of the balloon, wherein an opening of either one of the fluid supply sub lumen and the fluid drainage sub lumen is located on the distal end side from an intermediate location in an axial direction in the expansion portion, and wherein an opening of the other of the fluid supply sub lumen and the fluid drainage sub lumen is located at a proximal end of the expansion portion or in a vicinity thereof.