A bonding apparatus configured to bond a first substrate and a second substrate includes: a first holder configured to hold the first substrate; a second holder disposed to face the first holder in a vertical direction, and configured to hold the second substrate; a processing vessel accommodating the first holder and the second holder therein; and a horizontal position adjuster provided outside the processing vessel and connected to the first holder via a support supporting the first holder, the horizontal position adjuster being configured to adjust a horizontal position of the first holder.