The present invention provides a tire assembly, a tire monitoring system, a tire monitoring method, and a power generation body having a simple structure. This tire assembly is provided with: a tire attached to a wheel; a power generation body disposed on the inside of the tire; and an electronic device that receives the supply of power output from the power generation body. The power generation body has a first insulating film, a second insulating film, a first electrode, and a second electrode. The first insulating film has a first surface. The second insulating film has a second surface that faces the first surface and is in contact with the first surface. The first electrode has conductivity and is in contact with the back surface of the first surface of the first insulating film. Thesecond electrode has conductivity and is in contact with the back surface of the second surface of the second insulating film. The actual contact area between the first surface and the second surfacevaries in accordance with the deformation of the tire. The first insulating film and the second insulating film are configured such that one is positively charged and the other is negatively charged by changing the real contact area. By charging the first insulating film and the second insulating film, a voltage is generated between the first electrode and the second electrode, and power is output.