Provided is a device of bonding substrates together, which includes a first holding unit configured to vacuum-draw a first substrate and to adsorptively hold the first substrate on a lower surface thereof and a second holding unit installed below the first holding unit and configured to vacuum-draw a second substrate and to adsorptively hold the second substrate on an upper surface thereof. The second holding unit includes: a body portion configured to vacuum-draw the entire surface of the second substrate; a plurality of pins installed on the body portion and configured to make contact with a rear surface of the second substrate; and a support portion installed on the body portion at the outer side of the pins, the support portion having a reduced contact area over which the support portion makes contact with an outer peripheral portion of the second substrate.