An object of the present invention is to provide a burner having variable output structure that maintains the speed of a mixture injected through flame holes at a predetermined speed or more by supplying gas through a gas valve at a predetermined pressure or more, and prevents the occurrence of backfire at a low output by adjusting an opened area of the flame holes. In order to achieve the object, according to the present invention, a burner having variable output structure includes a flame-hole plate that includes a plurality of flame holes formed on the surface thereof exposed to a combustion chamber, and a flame hole adjusting unit that changes an output by adjusting the size of each flame hole according to load required in a combustion device.