A communication device for transmitting and receiving frames, which is capable of preventing an overflow of a buffer memory due to clock error even when the utilization factor of a transmission line is high. A frame holding section stores frames awaiting transmission. A transmission section sequentially takes out each frame from the frame holding section and outputs the frame to the transmission line, based on a control signal indicative of timing for transmitting the frame. A transmission control section initially outputs the control signal at a repetition period of T clocks (T≧2) and acquires the number of waiting frames in the frame holding section every N×T clocks (N≧2). When the number of waiting frames is equal to K (K≧1), the transmission control section makes some of transmission intervals shorter than T clocks to thereby output the control signal N+K times during next N×T clocks