In a glove door-installed knee air bag apparatus, a stud bolt of an inflator is fixed to an inflator supporting member in a state that the stud bolt is inclined in a vertical direction relative to a general plane of a glove door inner member. Due to the structure, a thickness W0 of an air bag module measured at the inflator installing portion is made small. The inflator supporting member includes a first portion and a second portion. In a case where a hook portion is formed in the first portion, the number of parts can be reduced. In a case where the inflator is located at a lower portion of a housing space, a handling force for opening and closing the glove door is light. In a case where the first portion comprises a bottom wall of the air bag casing and the second portion comprises a side wall of the air bag casing, the number of parts is reduced.