To operate discharge and collection of a large volume of casting sand falling in the solution treatment furnace fast and effectively.

This solution treatment furnace 1 is provided with a transport device 10 to transport a casting and a mold W through out a high temperature atmosphere in the furnace, an air current circulation device 30 to form a circulation air current in the furnace, and a sand grain discharge device S1 to discharge a casting sand of a mold dropped freely in a hearth zone out of the furnace. Plural hoppers S are disposed at a downward area of the transport device, and receive the casting sand freely dropped from the transport route of the casting and the mold. An air pressure type conveyer device 20 is arranged at a convergency part of the hoppers to send out the sand grain to the sand grain discharge device in the hoppers. The air pressure type conveyer device is provided with air pressure chambers 22, 23, into which a given flow volume of a high temperature air is supplied and multi aperture plates 27, 29 to form a top wall of the air pressure chamber and discharge an air current flowed into the chamber upwards. The multi aperture plate fluidizes the sand grain piled up on the plate and sends out the sand grain to the sand grain discharge device.