A recording-density control method of an image recording apparatus for performing image recording by arranging, a nozzle array component arranged in a plural number comprising a plurality of nozzles for discharging uniform-color ink. The bearing is lubricated with oil by means of two nozzles. Noise floor is isolated and the power of the noise floor may be computed to provide an estimate of random jitter variance, from which the standard deviation may be calculated. A brake mechanism locked and unlocked by tilting a display. A bottomed screw hole is provided to at least one end of the shaft to screw a headed screw for attaching a thrust plate a lubricating fluid is filled in a gap of a screw portion between the screw and the screw hole or a screw non-occupied space, and an interposing member which reduces a void cubic content in the screw non-occupied space is attached to the screw non-occupied space.