An image forming apparatus comprising an image data inputting device for inputting image forming data to the image forming apparatus, a control unit for adjusting operational conditions such as an amount of light of a light source, an insertion amount of color filters into a light path and so on in the image forming appartus for performing the copying processes on the basis of the image forming data and a mode switching unit for selecting one of a first mode for roughtly inputting the image forming data and a second mode for minutely inputting the image forming data. For an adjustment of a color balance, the image forming data inputting device comprises a first input unit for inputting a first data representing a color selected from a first color gradation and a second input unit for inputting a second data representing a color selected from a second color gradation, the first and second color gradations being defined between red and green and between yellow and blue, respectively, and the control unit adjusts the color balance of the image to be copied on the basis of the first and second data to obtain the copied image having a desired color balance.