Disclosed is an apparatus for acquiring initial frame timing in a communication system having a normalizer that calculates a normalized window power from powers of samples of received signal during a monitoring period, a cross power calculator that calculates a window cross power from cross powers of the samples during the monitoring period, and each cross power corresponds to multiplication of two of the samples, a divider that divides the window cross power by the normalized window power and outputs a metric for a sample corresponding to the monitoring period, and a peak-value detector that searches a sample having the maximum value among metrics for the samples of the received signals during a predetermined period, and the metrics are calculated by shifting the monitoring period, with a sample next to the sample searched by the peak-value detector being determined as a starting point of a frame.