A gas supply mask apparatus allows a mask wearer to inhale a gas such as oxygen gas such that air in a mask main body does not much mix in the gas approaching substantially lower ends and the vicinities of the nostrils of the mask wearer in the mask main body. In this gas supply mask apparatus, a gas introduction opening for introducing a gas such as oxygen gas and water vapor into the mask main body includes a first gas introduction opening capable of introducing the gas in, e.g., a bundle-like state into the mask main body, and a second gas introduction opening capable of introducing the second gas into the mask main body so as to surround, in a substantially ring-like state, the above-mentioned, first gas in a bundle-like state introduced into the mask main body from the first gas introduction opening.