1. An assignment method of terminals of a semiconductor package executed by an assignment supporting apparatus that assigns, to each of a plurality of pads of a semiconductor chip, one of a plurality of terminals provided at prescribed positions of a package substrate to which the semiconductor chip is jointed, the method comprising: deciding a maximum allowable distance to be a constraint condition regarding a relative distance between each of the pads and a terminal to be assigned to the pad by using a data processing unit of the assignment supporting apparatus, and extracting one or a plurality of assigned terminal candidates for each of the pads so that the relative distance between each of the pads and a terminal selected for the pad falls within a range of the maximum allowable distance by using the data processing unit; and performing a process to decide one of the terminals as a assigned terminal based on the assigned terminal candidates and assign the one of the terminals to one of the pads by using the data processing unit; wherein the process is a process to assign one of the terminals with priority to a pad having a smallest number of assigned terminal candidates in a not-assigned condition based on the assigned terminal candidates.