There is provided a communication system which is capable of resetting sub-communication ICs without providing special reset signal lines for transmitting a reset signal and also capable of properly transmitting a communication reset signal to the sub-communication ICs to reset the same when the system is in an abnormal state or when the power supply is turned off, an image forming apparatus provided with this communication system, an initialization method, and a storage medium that contains a program for executing the method. A host CPU controls the whole communication system. A communication controller controls a serial communication. A plurality of sub-communication ICs transmit serial data between themselves and the communication controller. A first reset IC resets the host CPU, and a second reset IC rests the communication controller. The first and second ICs reset the host CPU and the communication controller, respectively, according to different setting conditions. More specifically, the first reset IC resets the host CPU when the power supply voltage of the communication system is lower than a first predetermined value, and the second reset IC resets the communication controller when the power supply voltage is lower than a second predetermined value that is lower than the first predetermined value.