A debug system scans a scan memory element group having a plurality of scan memory elements which are connected in series in a semiconductor integrated circuit device and collects data in the scan memory element group. The semiconductor integrated circuit device has an end code register which is provided between an input terminal and an input side of the scan memory element group and holds an end code, a start code register which is provided between an output terminal and an output side of the scan memory element group and holds a start code, and a scan control circuit which controls shift operations of the scan memory element group, the end code register and the start code register, and outputs scan data to the output terminal.