A tire assembly (7, 7a, 7b, 7c 7d) comprising: a tire ( 70, 70A) attached to a wheel (FL, FR, RL, RR); a power generation body ( 1, 1A) that is arranged inside of the tire ( 70, 70A); and an electronic device (81,82,83) configured to receive a supply of electrical power output from the power generation body ( 1, 1A), the power generation body ( 1, 1A) comprising: a first member (10, 10A) having a first base material, a first electrode, and a first insulating film forming a first surface; a second member (20, 20A) having a second base material, a second electrode, and a second insulating film forming a second surface that opposes the first surface and comes into contact with the first surface; a cushioning material ( 30, 30A) arranged on a side opposite to the first surface of the first member (10, 10A); and a plate-shaped weight (40, 40A) that is arranged between the cushioning material ( 30, 30A) and the first member (10, 10A) and forms a pressing surface that presses the first member (10, 10A); wherein the power generation body ( 1, 1A) is arranged inside of the tire ( 70, 70A) such that the second member (20, 20A) is on the outer side in the radial direction of the tire ( 70, 70A) and the first member (10, 10A) is on the inner side in the radial direction of the tire ( 70, 70A), wherein the first member (10, 10A) and the second member (20, 20A) are configured such that a real contact surface area between the first surface and the second surface changes according to pressure applied to the first member (10, 10A) and the second member (20, 20A), and one of the first insulating film and the second insulating film is positively charged and the other is negatively charged due to the real contact surface area changing. a tire ( 70, 70A) attached to a wheel (FL, FR, RL, RR); a power generation body ( 1, 1A) that is arranged inside of the tire ( 70, 70A); and an electronic device (81,82,83) configured to receive a supply of electrical power output from the power generation body ( 1, 1A), the power generation body ( 1, 1A) comprising: a first member (10, 10A) having a first base material, a first electrode, and a first insulating film forming a first surface; a second member (20, 20A) having a second base material, a second electrode, and a second insulating film forming a second surface that opposes the first surface and comes into contact with the first surface; a cushioning material ( 30, 30A) arranged on a side opposite to the first surface of the first member (10, 10A); and a first member (10, 10A) having a first base material, a first electrode, and a first insulating film forming a first surface; a second member (20, 20A) having a second base material, a second electrode, and a second insulating film forming a second surface that opposes the first surface and comes into contact with the first surface; a cushioning material ( 30, 30A) arranged on a side opposite to the first surface of the first member (10, 10A); and wherein the first member (10, 10A) and the second member (20, 20A) are configured such that a real contact surface area between the first surface and the second surface changes according to pressure applied to the first member (10, 10A) and the second member (20, 20A), and one of the first insulating film and the second insulating film is positively charged and the other is negatively charged due to the real contact surface area changing.