An error detecting method and apparatus may be provided for a moving image transmitting system. An error detection code may be generated for each data block of a frame. The generated error detection code may be inserted into a byte alignment code of the data block. The frame may then be transmitted from a transmitting side to a receiving side. A byte alignment code may be extracted from each data block after the frame is received at the receiving side. Errors may be detected based on the extracted code. The method may enable a moving image encoder to be stably operated and allow improvement of the picture quality. Also, the method may allow the byte alignment code, which has been regarded as meaningless information, to be associated with a channel code so as to enhance error detection efficiency.