A cubic metric calculator performs a calculation of a time average of power of the amplitude of a transmission signal when a cubic metric value is calculated as a product-sum operation between a transmission power-dependent term including an amplitude value depending on the transmission power of a transmission signal and a time average term including only a modulation parameter not depending on the transmission power of the transmission signal. When the transmission signal is transmitted, the operator inputs the amplitude value to calculate the transmission power-dependent term, reads the value of the time average term from coefficient memory, and performs the product-sum operation using an operation result of the transmission power-dependent term and the read value of the time average term, thereby calculating a time average of the power of the amplitude of the transmission signal.