In a case where there are developers belonging to Life Rank 1 representing a service life substantially as long as that of a fresh developer (Step S501), and the developers includes one which is ready to print (Step S502), it is determined that image formation can be performed without performing a preparatory operation (Step S506). In a case where there is no print-ready developer but a developer which requires an agitation operation of rotating a developing roller by a predetermined quantity (Step S503), the agitation operation is performed on the developer (Step S504) so as to make the developer in a print-ready state. In a case where the developer cannot be made print-ready by the agitation operation, a density control operation for adjusting operating conditions of an apparatus is performed (Step S505). Thus is obviated an unnecessary operation. The developer subjected to a predetermined print preparatory process is used in a printing operation so that an image of good quality may be formed. In a case where no Rank-1 developer is available but a Rank-2 developer, deteriorated to a degree, is available, the same procedure is taken.