PURPOSE: To provide a tire fitting device by which tire fitting is performed surely and operation efficiency is improved, by performing automatically a pressurization work suited to a tire size.

CONSTITUTION: A tire fitting device is provided with a tire outer diameter measurement device comprising a pair of measurement arms 7 for sandwiching the outer diameter of a tire T on a conveyor and a cylinder 9 for operating the measurement arms in the diametral direction, and a tire pressurization device 6 comprising a plurality of pressurization rollers 14a-14c which abut equally on a plurality of parts on the tire outer diameter to rotate and pressurize the tire, a motor 15 for driving rotation of one of the pressurization rollers, and a cylinder 16 for operating expansion/contraction of the pressurization roller. And a controller 20 is provided to adjust pressurizing force according to a tire outer diameter by controlling the cylinder for operating expansion/ contraction of the pressurization roller based on outer diameter measurement signals detected by cylinder strokes for operating measurement arms.