When carrying out monochrome printing, an engine unit of a printer calculates an amount of toner consumed as lubricant by a color photoreceptor according to the number of sheets to be printed (S63). When carrying out color printing, the engine unit calculates an amount of toner remaining on the color photoreceptor after the printing based on an amount of toner necessary for printing calculated from a printing rate and an amount of actually transferred toner that is calculated from the transfer rate (S65). The toner remaining on the color photoreceptor is used as lubricant, and the engine unit calculates an amount of toner by subtracting the residual toner amount from the amount of toner as lubricant calculated from the number of sheets for monochrome printing (S67), and supplies the calculated amount of toner as lubricant to the color photoreceptor when carrying out monochrome printing.