An encoder includes a separation unit separating image data into a plurality of data blocks, a variable length encoding unit variable-length-encoding the data blocks separated by the separation unit so as to generate variable length code sequences, a code block generating unit generating code blocks variable-length-decoded in parallel from a start end and a termination end by combining two variable length code sequences generated by the variable length encoding unit, and a bit stream generating unit generating a bit stream such that a boundary between the code blocks is recognized.