PURPOSE: To improve the quality of an image by controlling an image forming condition according to paper thickness.

CONSTITUTION: A filler 39 which is provided in a paper carrying path 38 leading to an image forming part and which descends by the weight of a paper P, filler descending amount detection sensors 46a and 46b detecting the descending amount of the filler 39, a calculation means calculating the thickness of the paper P based on the outputs of the sensors 46a and 46b, a control means controlling the image forming condition to be a prescribed value suitable for the paper thickness based on the paper thickness calculated by the calculation means, and an alignment control means detecting the paper P based on the outputs of the sensors 46a and 46b and deriving timing for feeding the paper so as to align the image on the photoreceptor 30 of the image forming part with the paper P are provided. Then, the image forming condition is controlled based on the thickness of the paper P.