A vacuum forming machine includes a holder arranged to hold a decorative sheet, upper and lower boxes separated by the decorative sheet and the holder, a pressure reducer arranged to reduce pressures inside the upper and lower boxes, a first valve arranged to adjust a degree of pressure reduction inside the upper box, a second valve arranged to adjust a degree of pressure reduction inside the lower box, a heater arranged to heat the decorative sheet, a temperature information collector arranged to collect temperature information about the temperature of the decorative sheet, and a controller programmed to control opening/closing operations of the first and second valves by reference to the temperature information while the pressure reducer is operating.