A gas supply mask apparatus has low possibility that a gas rising in a mask main body will flow out from the upper end and the surrounding vicinity of the mask main body and give discomfort to the eyes of a mask wearer. In this gas supply mask apparatus, an angle formed between a direction in which a gas introduction opening faces and a virtual vertical plane facing right frontways falls within the range of 30° to 60° (preferably, the range of 35° to 55°, and more preferably, the range of 40° to 50°) when the mask main body is viewed right sideways.
