PURPOSE: To provide the function circuit block mechanism by which the technique of the field can add a simple control system, which is completely isolated from the main sequencer operating the whole of factory automation with respect to circuit, at the time of constituting a control mechanism for spaces generated in the factory automation.

CONSTITUTION: A comparator, a level checker, a multimotion detector, etc., required as block functions in the factory automation are constituted as a function circuit block and are built in a block function box having the same structure. The block function box B consists of a universal substrate 1, a terminal board A, a base frame 4, and a substrate cover 3 which projects from the base frame 4 and covers the periphery of the universal substrate 1, and an indicator lamp space 5 is formed between the terminal board A and the base frame 4.