A DCDC converter includes a signal splitting unit that splits an input signal into N signal components; N DCDC converter elements that process individually the N split signals; and an adder that adds outputs from the plural DCDC converter elements to generate output signals. Each of the DCDC converter elements has an operation band narrower than an applicable frequency band of the input signal, and selects a design parameter that allows a conversion efficiency of the DCDC converter elements to be optimized for any band of the applicable frequency bands. For example, the parameter of a PMOS transistor and a NMOS transistor, which configure an inverter is designed to optimize the efficiency at any of frequency bands. The frequency band of the input signal is split, and each of the split outputs is input to a DCDC converter element that has a corresponding frequency and high efficiency characteristic.