A drum brake apparatus comprising: a pair of brake shoes (25, 27) disposed so as to face an inner peripheral surface of a brake drum and movably supported on a backing plate; a wheel cylinder which is interposed between adjacent ends on one sides of the pair of brake shoes (25, 27) and configured to expand the pair of brake shoes (25, 27) by pushing the adjacent ends of the pair of brake shoes (25, 27) at a tip portion of a first piston and a tip portion of a second piston by fluid pressure; an extension mechanism which is disposed between a rear end portion of the first piston and a rear end portion of the second piston in the wheel cylinder and configured to rotate in one direction to drive the first piston and the second piston in a direction away from each other; and an electric actuator configured to rotate the extension mechanism, characterized in that the extension mechanism includes a drive gear and a nut member, wherein the drive gear is to be rotated by a drive shaft of the electric actuator, and wherein a female screw, a bearing portion and a straight gear are provided on the nut member, wherein the female screw portion which is screwed to a male screw portion coaxially provided at the rear end portion of the first piston is provided on one end side of the nut member, wherein the bearing portion which rotatably contacts with the rear end portion of the second piston is provided on the other end side of the nut member, and wherein the straight gear which is engaged with the drive gear is provided in an outer periphery of the nut member, and wherein at least the male screw portion and the female screw portion in the extension mechanism communicate with a liquid chamber of the wheel cylinder. a pair of brake shoes (25, 27) disposed so as to face an inner peripheral surface of a brake drum and movably supported on a backing plate; a wheel cylinder which is interposed between adjacent ends on one sides of the pair of brake shoes (25, 27) and configured to expand the pair of brake shoes (25, 27) by pushing the adjacent ends of the pair of brake shoes (25, 27) at a tip portion of a first piston and a tip portion of a second piston by fluid pressure; an extension mechanism which is disposed between a rear end portion of the first piston and a rear end portion of the second piston in the wheel cylinder and configured to rotate in one direction to drive the first piston and the second piston in a direction away from each other; and an electric actuator configured to rotate the extension mechanism, characterized in that the extension mechanism includes a drive gear and a nut member, wherein the drive gear is to be rotated by a drive shaft of the electric actuator, and wherein a female screw, a bearing portion and a straight gear are provided on the nut member, wherein the female screw portion which is screwed to a male screw portion coaxially provided at the rear end portion of the first piston is provided on one end side of the nut member, wherein the bearing portion which rotatably contacts with the rear end portion of the second piston is provided on the other end side of the nut member, and wherein the straight gear which is engaged with the drive gear is provided in an outer periphery of the nut member, and wherein at least the male screw portion and the female screw portion in the extension mechanism communicate with a liquid chamber of the wheel cylinder.