In a signal generation device in a wires transmission system, a calculation amount is greatly reduced compared with a convention FFT Pre-Processing method which performs oversampling, and peak power is reduced to substantially the same extent as in the convention method. A transmitter 100 includes a slope estimation unit 102 and a slope reference attenuation signal selection unit 103. The slope estimation unit 102 generates and outputs a slope estimation value indicating an inclination of a data signal waveform at a data signal point. The slope reference attenuation signal selection unit 103 estimates a data signal which may cause a peak after oversampling, based on an amplitude value of a data signal and a slope estimation value, and determines an attenuation amount for a selected data signal. The slope reference attenuation signal selection unit 103 generates information concerning a selection result and the determined attenuation amount, and outputs the information as a data attenuation coefficient.