A signal processing device capable of performing a process of reducing peak power without interfering with a transmission signal at a high speed is provided. A signal processing device includes a peak-reduced signal generating device and a band pass filter. The peak-reduced signal generating device divides an input signal having an information component into signal streams for every predetermined number of signals, and generates peak-reduced signal with peak canceling signals on the basis of the signal streams. The peak-reduced signal generating device combines the signal streams which the peak-reduced signals on the basis of an order in which the division into the signal streams has been performed. The band pass filter passes a frequency component corresponding to the information component and rejects a frequency component corresponding to the peak canceling signal with respect to a signal based on a signal from the peak-reduced signal generating device.