Method for detecting transmission power faults in cellular telephones without detecting transmission power. A microcomputer compares a criteria B with an absolute value |Pi-Pc| of the differential between initial transmission power value Pi and transmission power concentration value PC. A transmission power fault is determined to have occurred when the absolute value 51 Pi-Pc| is larger than criteria B (|Pi-Pc|B), so transmission power faults can be detected without detecting the transmission power.