The invention is intended to provide a building sequence planning system for an automobile production line, which can prepare an efficient building sequence. The system comprises an input unit (1) for inputting information of vehicles to be manufactured, a processing unit (3) for deciding an optimum building sequence based on the vehicle information inputted through the input unit (1), and an output unit (5) for externally outputting a building sequence schedule decided by the processing unit (3). The processing unit (3) prepares a vehicle building sequence, determines a degree of dissatisfaction of the prepared building sequence, as a penalty value, in accordance with restriction conditions which are inputted through the input unit (1) and are imposed when building the vehicles into work, and decides a building sequence with a minimum penalty by preparing a plurality of building sequences and determining the penalty value for each building sequence with respect to the restriction conditions.