Image forming apparatus

An output device that outputs a transmission signal to a transmission line, comprising:

• an impedance matching section including an impedance adjustment section, and a dummy circuit section having the same configuration as the impedance adjustment section and adapted to calculate an adjustment value for matching an output impedance to a characteristic impedance of the transmission line, the impedance matching section being configured to set the adjustment value calculated by the dummy circuit section to the impedance adjustment section to match the output impedance to the characteristic impedance;
• a switching transistor connected in series to the impedance matching section and configured to be turned on/off so as to switch an output between an H level and an L level;
• and
• a constant current driver configured to add a constant current to the output.