PURPOSE: To reduce the equipment costs greatly and lessen the space for installation of facilities by forming a duct for the cooling wind for a frozen object layer in the floor part where the frozen object layer is formed, and through this duct, flowing the low temp. gas of low temp. material gasified in the accommodation part.

CONSTITUTION: An airtight accommodation room 7 is furnished to accommodate dry ice D, which is sublimated to generate low temp. carbon dioxide gas G. A forward path 8a is provided to lead this gas G to the top of a duct 5, while a return path 8b is furnished to return the gas G after passing through the duct 5 back to the accommodation room 7 from the bottom of the duct 5. In the forward path 8a, a circulation fan 9 is interposed to circulate the gas G forcedly from the accommodation room 7 to the forward path 8a, snow layer cooling duct 5, and return path 8b. That is, heat is absorbed from an ice layer 2 and snow layer 3 to cool them, and thereby melting of these layers is prevented, and thus snow layer 3 to form the ski gliding surface is maintained.