In a high frequency generator, a high frequency generated by an IQ modulation of a vector multiplier and a amplification of an amplifier is outputted through an output unit. An directional coupler outputs a first high frequency including a part of traveling waves and a second high frequency including a part of reflected waves. A control units obtains an estimated value of each of an in-phase component and an orthogonal component of the traveling waves in the output unit, and an in-phase component and an orthogonal component of the reflected waves in the output unit by performing a first matrix operation that is an operation of four polynomials, each including as multi-variables an in-phase component and an orthogonal component of a first high frequency and an in-phase component and an orthogonal component of the second high frequency.