A combustor according to the invention includes a combustor basket to which air A is supplied from the outside, a plurality of first nozzles that are annularly provided along the inner periphery of the combustor basket and that supply premixed gas M of the air and fuel to the inside of the combustor basket, and a transition piece in which the combustor basket is connected to a base end thereof and which burns the premixed gas supplied from the first nozzles, thereby forming a flame front spread to the outer periphery side toward the leading end in an axial direction, wherein each first nozzle supplies the premixed gas with fuel concentration changed around the center axis of the first nozzle such that the flame front has a uniform temperature in the axial direction.