A highly-reliable combustor is provided that allows flash back of flame into a premixer to be suppressed.The combustor has a mixing chamber forming member 110 that forms a mixing chamber thereinside. The mixing chamber includes a first mixing chamber 200 broadening toward a downstream side. The member 110 includes air introduction holes 202, 203, 204 formed in a plurality of rows in an axial direction, with the air introduction holes being arranged plurally in a circumferential direction of the mixing chamber. The member 110 includes a fuel ejection hole 206 provided in a wall surface which forms the air introduction hole. The air introduction holes 202, 203, 204 are circumferentially eccentrically installed. The air introduction holes 202 located in the most upstream row are more inclined toward the downstream side than the air introduction holes 203, 204 located in the rows other than the most upstream row.