A processing device for processing a sheet material with a pattern of the present invention is such as a sewing machine with pattern matching operation. The processing device has a detecting unit for detecting a color state of the pattern of the sheet material and producing a color state signal indicative of the color state. The processing device processes the sheet material on the basis of the color state signal produced by said detecting means. According to the present invention, the processing device is provided with an automatic adjusting unit for adjusting the detecting unit to allow the detecting unit to produce a desired color state signal with respect to a reference color state. Therefore, the white balance or the dynamic range is properly adjusted simply and reliably for the processing device.