A substrate test apparatus is provided that can measure a dechucking force with high reliability. The substrate test apparatus includes an electrostatic chuck, a normal-force measuring unit disposed on the electrostatic chuck to be capable of pushing or pulling the substrate vertically, an electrostatic-chuck power supplying unit for applying a driving voltage and a first ground voltage to the electrostatic chuck, and a substrate power supplying unit for applying a second ground voltage to the substrate, wherein the substrate test apparatus performs steps including applying the driving voltage to the electrostatic chuck and charging the substrate by applying the second ground voltage to the substrate, subsequently discharging the substrate by applying the first ground voltage to the electrostatic chuck and by applying the second ground voltage to the substrate, and subsequently measuring a dechucking force of the substrate by pulling the substrate vertically by the normal-force measuring unit.