task 51 in an operating state to allow execution of the action when the conditions are satisfied in task 51 in addition to the condition and action table 52 a signal table 53 consisting of the following elements is accessed 1 reading the di signal value and setting the value in the signal table 53 as the 34 current signal value 34 2 calculating the remaining signal values of the 34 signal values to be used in condition evaluation 34 from the 34 current signal value 34 and the 34 preceding signal value 34 3 sequentially examining the condition and action table 52 establishing a flag in the 34 signal values to be used in action output 34 when the action corresponding to a satisfied condition is signal output and when it is task activation erasure finishing its operation at this stage 4 determining the current signal output in accordance with the priority order of actions and effecting the signal output the priority order of actions is predetermined for instance in the following manner the following program interfaces built in functions are prepared to facilitate by means of a high level language procedural signal processing for general purpose signal processing that requires only a moderate processing speed a waiting in a synchronized state until the signal is turned on b waiting in a synchronized state until the signal.