Provided is a substrate testing apparatus capable of adjusting a substrate to a desired temperature. A prober (10) is provided with: a stage (11), upon which a wafer (W) on which a semiconductor device has been formed, is placed; a testing head (14) which tests electrical properties of the semiconductor device on the placed wafer (W); a temperature adjustment system (25) which adjusts the temperature of the stage (11); and a temperature adjustment flow path (28) which passes through the stage (11). The temperature adjustment system (25) has: a high-temperature chiller (26) which supplies a high-temperature medium to the temperature adjustment flow path (28); a low-temperature chiller (27) which supplies a low-temperature medium to the temperature adjustment flow path (28); and a mixing valve unit (29) which mixes the high-temperature medium and the low-temperature medium which are supplied to the temperature adjustment flow path (28).