PURPOSE: To uniformalize the production of a unit by providing an arithmetic means for computing the lead time according to the condition of a difference when the producing operation setup and the assembling operation setup differ from each other.

CONSTITUTION: In a shift determining part 27, if it is determined that there is a shift difference shown in a pattern A or a pattern B, the lead time is reloaded with a value obtained by adding the number of machines to be assembled per shift of an assembly 1 line or an assembly 2 line to a reference lead time retrieved by a process depth retrieving part 26. With the above operation, according to the lead time, a production instruction for a unit is given to a unit production instructing processing part 15. If it is decided that there is shift difference shown in a pattern C or a pattern D by the shift determining part 27, the shift difference condition is output to a double speed instructing processing part 29.