A radio-frequency identification (RFID) tag includes: a plate-shaped sealing piece made of an elastic material. An inlet is enclosed within the sealing piece. The inlet includes an electronic component and an antenna connected to the electronic component. A pair of reinforcing pieces are located respectively on the front and back surfaces of the sealing piece so as to sandwich the electronic component. The reinforcing pieces are made of a first material harder than the elastic material. A joint piece configured to couple the reinforcing pieces to each other. The joint piece is made of a second material harder than the elastic material.