An image forming apparatus capable of observing toner amount limitation with reliability even when two types of developers which have the same have and have different densities is provided. After an inputted image signal is subjected to color conversion processing to make the toner amount limitation, at least one color signal of the converted color signals is converted into signals for a dark color toner and a light color toner by light and dark separation using a single light and dark separation look-up table. Thereafter, the toner amount is determined again for each pixel. In the case where the toner amount exceeds a predetermined value, the light and dark separation of at least one color is made until the toner amount is the predetermined value or less by using another light and dark separation look-up table.