A production of voids between substrates is prevented when the substrates are bonded together, and the substrates are bonded together at a high positional precision while suppressing a strain. A method for bonding a first substrate and a second substrate includes a step of performing hydrophilization treatment to cause water or an OH containing substance to adhere to bonding surface of the first substrate and the bonding surface of the second substrate, a step of disposing the first substrate and the second substrate with the respective bonding surfaces facing each other, and bowing the first substrate in such a way that a central portion of the bonding surface protrudes toward the second substrate side relative to an outer circumferential portion of the bonding surface, a step of abutting the bonding surface of the first substrate with the bonding surface of the second substrate at the respective central portions, and a step of abutting the bonding surface of the first substrate with the bonding surface of the second substrate across the entirety of the bonding surfaces, decreasing a distance between the outer circumferential portion of the first substrate and an outer circumferential portion of the second substrate with the respective central portions abutting each other at a pressure that maintains a non-bonded condition.