Functional analysis of mutations in SLC7A9, and genotype–phenotype correlation in non-Type I cystinuria

An image forming apparatus is provided, which comprises a developer container for containing developer, a developer amount detector for detecting an amount of the developer contained in the developer container, a pixel number counter for counting the number of pixels required for forming an image, a sheet number counter for counting the number of sheets of a recording material on which an image is formed and a calculator for calculating the printable number of sheets from the present onward using the developer amount detected by the detector, the number of pixels counted by the pixel number counter and the number of sheets counted by the sheet number counter.