When an image forming apparatus satisfies a condition to shift it to a power saving state, if a specific function that needs to respond to an inquiry from an external apparatus within a predetermined time is set, a power control unit shifts the image forming apparatus to a first power saving state in which power is supplied to a control unit configured to respond to the inquiry, and if the specific function is not set, shifts the image forming apparatus to a second power saving state in which no power is supplied to the control unit.

A communication device includes: a communication control section; a variable resistor; a voltage detecting section; and a resistance value adjusting section. The communication control section performs control necessary for facsimile communication. The variable resistor is arranged between two line-connecting terminals, each of the line-connecting terminals is for connecting a telephone line. The voltage detecting section detects a line voltage of the telephone line to which the variable resistor is connected under closed state of the telephone line. The resistance value adjusting section changes a resistance value of the variable resistor. When the changed resistance value of the variable resistor becomes a standard resistance value to be a voltage value where the line voltage detected by the voltage detecting section is capable of the facsimile communication, the resistance value adjusting section sets the resistance value of the variable resistor to a resistance value for the facsimile communication.

A communication device includes: a communication control section; a variable resistor; a voltage detecting section; and a resistance value adjusting section. The communication control section performs control necessary for facsimile communication. The variable resistor is arranged between two line-connecting terminals, each of the line-connecting terminals is for connecting a telephone line. The voltage detecting section detects a line voltage of the telephone line to which the variable resistor is connected under closed state of the telephone line. The resistance value adjusting section changes a resistance value of the variable resistor. When the changed resistance value of the variable resistor becomes a standard resistance value to be a voltage value where the line voltage detected by the voltage detecting section is capable of the facsimile communication, the resistance value adjusting section sets the resistance value of the variable resistor to a resistance value for the facsimile communication.

When an image forming apparatus satisfies a condition to shift it to a power saving state, if a specific function that needs to respond to an inquiry from an external apparatus within a predetermined time is set, a power control unit shifts the image forming apparatus to a first power saving state in which power is supplied to a control unit configured to respond to the inquiry, and if the specific function is not set, shifts the image forming apparatus to a second power saving state in which no power is supplied to the control unit.