A wafer bonding method includes: holding a first substrate with an upper holding mechanism 7 by applying a voltage to the upper holding mechanism 7; generating a bonded substrate by bonding the first substrate and a second substrate held with a lower holding mechanism 8; and dechucking the bonded substrate from the upper holding mechanism 7 after a voltage which attenuates while alternating is applied to the upper holding mechanism 7. By applying the voltage which attenuates while alternating to the upper holding mechanism 7, residual attracting force between the bonded substrate and the upper holding mechanism 7 is reduced, thereby enabling the bonded substrate to be dechucked from the holding mechanism more surely in a shorter time period. As a result, the first substrate and the second substrate can be bonded in a shorter time period.