To automatically reduce an electric consumption by dividing a composite material silo into a plurality of silos in the vertical direction, and independently controlling electric heaters every block in response to a storage level.

A composite silo 1 storing an asphalt mixture in a heating state is divided into a plurality of blocks 1A-1E in the vertical direction, and electric heaters 16, 16 every blocks 1A-1E are connected to a controller 18. The electric heater 16 is independently on-off-controlled by thermocouples 17... provided on each block 1A-1E at each set temperature. The controller 18 calculates a storing level, energizes to the electric heater 16 every block 1A-1E, and controls the temperature. Thereby an electric usage can automatically be reduced.