A signal power detection apparatus in which a power value can be detected at a high accuracy with a low power consumption includes a pulse generator for generating a timing pulse whose phase is sequentially shifted corresponding to an inputted data signal, a power computing circuit for obtaining the inputted data signal based on a timing pulse and computing a power value of the inputted data signal by squaring a voltage value of the inputted data, and an averaging circuit for averaging the power value of the computed inputted data. A power can be accurately detected without using a high-speed timing clock, and a power value can be detected at a high accuracy with a low power consumption.