PURPOSE: To exclude a request having the possibility destroying a device by writing and controlling a scanout data in block unit as to the device being the object of status change in the scan-in/scan-out system

CONSTITUTION: A write enable/disable bit to each block is provided in forming the flip-flop of a logical device LG into a block. For example, as for the 1st block, its head address is compared with a write enable/disable bit (0 or 1), and provided to the 1st block. A data is written to a scan memory SMC by a scanout SO instruction. When a rewrite data DT and a rewirte address AD are given next, this address is fed to a write mode table WMT, a block belonging to the address is recognized and a corresponding bit is known, allowing to discriminate write enable/disable. When write is enabled, a write enable signal WE is fed to the scan memory SCM, and the data is rewritten.