Substrate heating method

A substrate heating device includes: heating modules each having a processing vessel within which a heating plate is disposed, an gas inlet port for introducing a purge gas into a processing atmosphere, and an exhaust port for exhausting the processing atmosphere; individual exhaust paths each connected to the exhaust port of the heating modules; a common exhaust path connected to downstream ends of the individual exhaust paths of the heating modules; a branch path branched from the individual exhaust paths and opened to the outside of the processing vessel; and an exhaust flow rate adjusting unit configured to adjust a flow rate ratio of an exhaust flow rate of a gas exhausted from the exhaust port into the common exhaust path and an introduction flow rate of a gas introduced from the outside of the processing vessel into the common exhaust path through the branch path.