PROBLEM TO BE SOLVED: To provide a heating and humidifying device for a respiratory gas which is hardly affected by a temperature change from the outside, and can stably supply the sufficiently heated and humidified respiratory gas to a patient without causing dew condensation.SOLUTION: An interface connection hose 5 of a heating and humidifying device 100 for a respiratory gas includes: an air suction hose 21 sending the respiratory gas after heating and humidification to a patient interface 8 from a chamber 3 and a heat insulation flow passage 31 disposed in a state of surrounding the circumference of the air suction hose 21, and making heat-insulating air pass to keep the respiratory gas inside the air suction hose 21 warm. The heat insulation flow passage 31 includes: an inner flow passage 32 disposed in contact with the air suction hose 21 and an outer flow passage 33 disposed outside it. The inner flow passage 32 and the outer flow passage 33 are disposed while communicating with each other in one end part of the heat insulation flow passage 31. In the other end part of the heat insulation flow passage 31, an introduction port 34 for introducing the heat-insulating air into the inner flow passage 32 and a lead-out port 35 leading out the heat-insulating air from the outer flow passage 33, are disposed.
