A direct downconversion receiver combines a received RF signal and a local oscillator signal to form a combined signal. When a patch formed in an upstream image forming station and transferred onto the intermediate transfer belt and a patch formed on the surface of the photosensitive drum pass through the primary transfer portion, a passing bias different from the transfer bias is applied to the primary transfer portion. A periodic scheduled beacon message is transmitted with a unicast indication element and a multicast indication element. A microcontroller, which is part of the computer in the computer telephony system, is connected in controlling relation to the interface and to the interface logic. The enrichment control unit sets the degree of richness of the injected fuel to a first degree of richness that is greater than stoichiometry from the start of the enrichment process, and maintains the first degree of richness even after the output of the detection unit has reached a stoichiometric air-fuel ratio or richlean value.