A combustor includes a pilot fuel nozzle and a plurality of main premixing nozzles arranged therearound for forming a premixture of air and fuel supplied from a main fuel nozzle, and is improved so as not to cause vibratory combustion. Pilot fuel nozzle unit 104 comprises a plurality of pilot fuel nozzles 103. A plurality of main premixing nozzles 102 are disposed on a coaxial circumference of the pilot fuel nozzle unit 104. The pilot fuel nozzles 103 are arranged irregularly in a circumferential direction of the pilot fuel nozzle unit 104, so as to form portion 105 where there is no pilot fuel nozzle 103. Premature in the main premixing nozzles 102 positioned corresponding to the pilot fuel nozzle 103 burns with comparatively short flames. Premature in the main premixing nozzles 102 positioned corresponding to the portion 105 of no pilot fuel nozzle 103 burns with long flames because of flames spreading from adjacent main fuel nozzles. Thus, by differences in flame length, heat generation rate distribution is dispersed.