To provide a building material that can produce an environment suitable for divided spaces by utilizing the temperature difference between the spaces.

This building material is composed of an external wall main body 3 which partitions an indoor space 1 from an outdoor space 2, and Peltier elements 4, 5, and 6 provided on the surface side of the main body 3. The Peltier elements 4 and 5 generate electromotive forces based on the temperature difference between the spaces 1 and 2. On the indoor space 1 side of the main body 3, a red LED 5a, a blue LED 5b, and a green LED 5c are provided. The Peltier elements 4 are connected to a battery and the Peltier element 5 is connected to the LEDs 5a, 5b, and 5c through a controller 7. The Peltier elements 6 are connected to an external power source.