PURPOSE: To quickly and easily set and read the internal state by providing not only a means which scans FFs in a logical device with an address unique in the logical device but also a means which scans them with a common address.

CONSTITUTION: For example, plural channel devices 6 are provided in an input/ output processing device and the principal logic part of each device 6 is realized with an LSI. The scan address is set to an address register 11 in a scan control part 10. The set scan address is decoded by a decoder 12, which decodes scan addresses of individual devices 6, and a decoder 13 which decodes the scan address common to all devices 6. All devices are quickly initialized as block multiplexer channels by the output of the decoder 13, and a desired device 6 is quickly initialized as a byte multiplexer channel by the output of the decoder 12.