A room temperature bonding machine is provided with an evacuation apparatus, a gas supply apparatus, a pressure gauge, a cleaner apparatus, a pressure controller and a pressing mechanism. The evacuation apparatus evacuates gas from the chamber. The gas supply apparatus supplies introduction gas into the chamber. The pressure gauge measures the pressure in the chamber. The cleaner apparatus cleans first and second substrates in the chamber when said pressure is at a predetermined degree of vacuum. The pressure controller controls both of the evacuation apparatus and the gas supply apparatus so that the pressure is regulated to a target pressure. The pressing mechanism presses and bonds the first and second substrates when the pressure is set to said target pressure.