An output buffer circuit, a differential output buffer circuit, an output buffer circuit having a regulation circuit and a regulation function, and a transmission method, to improve resolution of a pre-emphasis amount without increasing power consumption or a circuit area. The output buffer includes a delay circuit, an inverter and output buffers to transmit a logical signal to a transmission line and generate a waveform having four or more types of signal voltages on a transmission side according to a signal attenuation amount of the transmission line. The output buffer has a selector and a variable resistance portion at an output resistance to change a pre-emphasis amount according to a change in a variable resistance value. The inverter is configured to select a signal to input into the output buffer, invert a data signal and adjust a tap pre-emphasis amount by a select signal of the selector logic.