1. A control apparatus for controlling a controlled object which includes a plurality of controlled elements, comprising: a host processor for supervising said control apparatus and for interpreting successive steps of subprograms included within a control program to generate commands for the control of said controlled elements in response to respective demand signals, each command including first designation information for designating a subprogram to be processed after the execution of said each command; a plurality of slave modules each slave module being allotted to one of said controlled elements, respectively, and includes a processor for interpreting and executing said commands to generate control signals for said allotted controlled element and for generating, upon completion of the execution of said each command, a demand signal for requesting said host processor to generator another one of said commands, said demand signal includes second designation information for designating a subprogram to the processed in said host processor; and communication means for transmitting said demand signals from said slave modules to said host processor and said commands from said host processor to said slave modules.