The ways of present transformer design can be divided into two types: using spreadsheet like Excel and using design software. Our first work is to develop the design software that can be used by small companies for free. We developed design software which generates as many designs as possible, without aid of expert's knowledge. Our second work is to improve efficiency by parallelizing the repetitive calculations. The performance of our design software is evaluated by comparing the results obtained from different numbers of cores. We show improvement of execution time where execution of 4 cores is about 45% faster than that of 1 core.