A wafer bonder for bonding wafers in a vacuum is disclosed. The wafer bonder comprises: a lower bonding unit; a upper bonding unit for pressurizing the wafers to bond when falling towards the lower bonding unit; a hollow bellows which are stretched while being connected to the upper bonding unit to allow the up-down direction displacement of the upper bonding unit; and a chamber housing for forming a vacuum chamber inside when a upper opening is being closed by the bellows and the upper bonding unit.
