A method for subjecting target substrates to a heat process under a vacuum pressure includes a transfer step, heating-up and pressure-reducing step, and heat-processing step. The transfer step is arranged to transfer into a reaction chamber a holder that supports the substrates at intervals. The heating-up and pressure-reducing step following the transfer step is arranged to heat up the reaction chamber to a process temperature, and exhaust the reaction chamber to a process pressure. During the heating-up and pressure-reducing step, the reaction chamber is set at the process pressure after being set at the process temperature, to form a state where the reaction chamber has the process temperature under a pressure higher than the process pressure. The heat-processing step following the heating-up and pressure-reducing step is arranged to subject the substrates to the heat process at the process temperature and process pressure.