To grasp, accurately and easily, the heat collection quantity from a heat collection source in a heat collection test.

A heat source test for allowing a heat medium W to pass through a heat collecting heat exchanger 2 and to execute heat exchange with the heat collection source 1 is executed under such plural conditions that the inlet heat medium temperature t1 of the heat collecting heat exchanger 2 is changed in a radiation region Rh having a higher temperature than the heat collection source temperature tg. A linear correlation m between the heat medium temperature t2 and the heat collection quantity q including a heat collection region Rc having a lower temperature than the heat collection source temperature tg is obtained, based on measurement data t1, t2 of the heat medium temperature obtained by the heat source test and a heat medium flow rate g.