A substrate bonding method for bonding two substrates, said method comprising: an activation treatment step wherein at least one of the bonding surfaces of two substrate, said bonding surfaces being to be bonded with each other, is activated by being subjected to at least either one of reactive ion etching with use of a nitrogen gas or irradiation of nitrogen radicals; a gas exposure step wherein the bonding surfaces of the two substrates are exposed to a gas that contains moisture within a predetermined base time after the activation treatment step; and a bonding step wherein the two substrates, the bonding surfaces of which are activated in the activation treatment step, are bonded with each other.