There is provided a communication system in which semi-duplex many-to-many multicasting service can be performed to both a mobile station and a base station by using a unified call control protocol such as SIP on an IP network, and can contain mobile stations and base stations of existing wireless facilities. The housing is shaped to rest against the chest of the person so that the direction of the light beam remains substantially stable. The integrated circuit designs are traversed net-wise and cut points are inserted at compare points that are matched and that are not determined to be constant. Upon focusing on an infinite object point, the fourth lens group G4 moves in a locus opposite to that of movement of the third lens group G3 during zooming. Because the sensor rotor of the magnetic pole position detecting portion is attached to the rotor and the sensor stator is adjacent to the stator and is fixed to the case, it is no longer necessary to use an all-round embracing type magnetic pole position detecting portion that embraces the entire shaft of an electric machine. When an off-line mode is selected via an operation panel of the sheet post-treatment equipment, a sheet post-treatment equipment controller notifies an engine controller of the image forming apparatus that this mode has been selected.