A substrate having an insulating layer including an oxide is loaded into a chamber, and at least a part of the insulating layer is removed by injecting a process gas including an etching source gas into the chamber. The removal process is performed in a pulse type in which a first period and a second period are repeated a plurality of times. The etching source gas is supplied at a first flow rate during the first period and is supplied at a second flow rate less than the first flow rate during the second period. A temperature of the inside of the chamber remains at 100° C. or more during the removal process.