A hydraulic power unit 15 of a match-plate molding machine comprises a hydraulic pump 20 for supplying oil, a piping system 21, 25, and 26 that fluidly communicates with first and second hydraulic cylinder systems 7 and 10 for supplying the oil from the hydraulic pump 20 to them to perform a squeeze step, an accumulator 22 that is provided within the piping system, first and second electromagnetic directional control valves 23 and 24 for controlling the flow of the oil from the hydraulic pump 20 to the first and second hydraulic cylinder systems 7 and 10, first and second pressure sensors 27 and 28 for measuring pressures of the oil of the first and second hydraulic cylinder systems 7 and 10, and for generating output signals that correspond to the measured value, and a controller 29 for receiving the output signals from the first and second pressure sensors 23 and 24, and for controlling the turns of the first and second electromagnetic directional control valves 23 and 24 based on the output signals and the predetermined value within a range below the pressure holding the accumulator 22 against the oil.