To easily detect a connection state of a toner density sensor at low cost.
This image forming device 1 is provided with the toner density sensors 15Y, 15M, 15C, 15K for outputting respectively respective detection signals KS based on toner densities in developing devices 13Y, 13M, 13C, 13K, an analog switch 31 having four toner density ports for inputting respectively the respective detection signals KS, four image density ports for inputting respectively respective density signals SI, and one output port, and for switching the respective toner density ports and the respective image density ports sequentially to the output port to be connected selectively, and a signal processing part 32 for processing a signal appearing in the output port. The respective detection signals KS and the respective density signals SI are connected to the respective toner density ports and the respective image density ports, to make each of the density signals SI appear in the output port in advance to each of the detection signals KS, when the analog switch 31 switches sequentially the connection.
ANDO HISAKUNI
WATANABE ISAO
TSUJIHARA KIYOTO
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