An image forming apparatus is able to form steady test-pattern toner
images for calibration of reflection density detection characteristics
with ample toner. The operation consists of forming a test-pattern toner
image for calibration of the reflection density detection
characteristics, which is formed of a plurality of toner images of
different colors aside from a reference test-pattern toner image for
controlling image forming conditions, detecting the detection
characteristics of a reflection density sensor from the result of
detection of the quantity of toner attached to the test-pattern toner
image for calibration of the reflection density detection
characteristics, and calibrating the output characteristics of the
reflection density sensor.