Subsequently, the CNV controller 13 compares the loss of the edge-alignment phase shift with the loss of the overlap phase shift. The CNV controller 13 calculates the phase shift amount θsft₀ from the on periods (on-duty periods) Duty1₀, Duty2₀ of the current period on the basis of the mathematical expression (1) (S14). Alternatively, the edge-alignment phase shift amount θsft₀ is called up from the shift amount map that defines the correlation between each of Duty1₀ and Duty2₀ and the edge-alignment phase shift amount θsft₀.

In addition, the CNV controller 13 estimates a loss at the time when the edge-alignment phase shift is executed by using the phase shift amount θsft₀ by consulting the loss map (S16).

The CNV controller 13 estimates a power loss due to the overlap phase shift in parallel with estimation of a power loss due to the edge-alignment phase shift. The CNV controller 13 calculates the overlap phase shift amount θsft from the on periods Duty1₀, Duty2₀ of the current period, the rates Rate1, Rate2, and the overlap period t on the basis of the mathematical expression (3) (S18). Alternatively, the edge-alignment phase shift amount θsft_t is called up from the shift amount map that defines the correlation between the edge-alignment phase shift amount θsft_t and each of Duty1₀, Duty2₀, Rate1, Rate2, and the overlap period t.

In addition, the CNV controller 13 estimates a loss at the time when the overlap phase shift is executed by using the phase shift amount θsft_t by consulting the loss map (S20).