PURPOSE: To enhance amenity for passengers seated on each seat by cooling each seat at the time of a cooling operation, and also warming up each seat at the time of a heating operation.

CONSTITUTION: A cooling and heating duct 26 is laid out along a great number of seats lined up at intervals in the longitudinal direction in a cabin, an air duct 14 communicated with an upper diffuser 18 is formed in the seat back 13 of each seat 10, and also an air duct 12 communicated with a lower diffuser 15 is formed in each seat cusion 11. At the time of a cooling operation, cold air having passed through the cooling and heating duct 26 is led to each air duct 14 by way of each connection duct 17 and each switching damper 16, each seat back 13 is then cooled, and the cold air is blown out of each upper diffuser 18 into the cabin 2 thereafter. At the time of a heating operation, warm air having passed through the cooling and heating duct 26 is led to each air duct 12 with each switching damper 16 switched, each seat cushion 11 is then warmed up, and the warm air is blown out of each lower diffuser 15 into the cabin 2 thereafter.