A flaskless molding machine forming a flaskless upper mold and lower mold, comprising: an upper flask; a lower flask disposed below the upper flask and capable of clamping a match plate with the upper flask; a lower flask drive unit configured to move the lower flask in a vertical direction; a lower filling frame disposed below the lower flask and having an upper opening capable of communicating with a lower opening of the lower flask; an upper plate capable of entering and being retracted from the upper opening of the upper flask; a lower plate capable of entering and being retracted from the lower opening of the lower filling frame; an upper flask oil-hydraulic cylinder coupled to the upper flask; a first oil-hydraulic circuit configured to move the upper flask oil-hydraulic cylinder in the vertical direction; a lower filling frame oil-hydraulic cylinder coupled to the lower filling frame; a second oil-hydraulic circuit configured to move the lower filling frame oil-hydraulic cylinder in the vertical direction; and the lower flask drive unit and a squeeze oil-hydraulic circuit configured to perform a squeeze process by moving the lower plate in an upward direction, characterized in that the first oil-hydraulic circuit includes a first back pressure circuit configured to apply, to the upper flask oil-hydraulic cylinder, a first back pressure serving as a resistance against an upward movement of the upper flask toward the upper plate during the squeeze process of the lower flask drive unit and the squeeze oil-hydraulic circuit, the first back pressure circuit includes an upper flask free electromagnetic valve configured to free oil flowing to the upper flask cylinder and an upper flask counterbalance valve configured to adjust the pressure of oil freed by the upper flask free electromagnetic valve, and the second oil-hydraulic circuit includes a second back pressure circuit configured to apply, to the lower filling frame oil-hydraulic cylinder, a second back pressure serving as a resistance against a downward movement of the lower filling frame toward the lower plate during the squeeze process of the lower flask drive unit and the squeeze oil-hydraulic circuit, the second back pressure circuit includes an lower filling frame free electromagnetic valve configured to free oil flowing to the lower filling frame oil-hydraulic cylinder and an lower filling frame counterbalance valve configured to adjust the pressure of oil freed by the lower filling frame free electromagnetic valve, wherein the first oil-hydraulic circuit and the second oil-hydraulic circuit adjust the balance between a squeeze force to the upper mold and a squeeze force to the lower mold using the first back pressure and the second back pressure achieved by the upper flask counterbalance valve and the lower filling frame counterbalance valve. an upper flask; a lower flask disposed below the upper flask and capable of clamping a match plate with the upper flask; a lower flask drive unit configured to move the lower flask in a vertical direction; a lower filling frame disposed below the lower flask and having an upper opening capable of communicating with a lower opening of the lower flask; an upper plate capable of entering and being retracted from the upper opening of the upper flask; a lower plate capable of entering and being retracted from the lower opening of the lower filling frame; an upper flask oil-hydraulic cylinder coupled to the upper flask; a first oil-hydraulic circuit configured to move the upper flask oil-hydraulic cylinder in the vertical direction; a lower filling frame oil-hydraulic cylinder coupled to the lower filling frame; a second oil-hydraulic circuit configured to move the lower filling frame oil-hydraulic cylinder in the vertical direction; and the lower flask drive unit and a squeeze oil-hydraulic circuit configured to perform a squeeze process by moving the lower plate in an upward direction, characterized in that the first oil-hydraulic circuit includes a first back pressure circuit configured to apply, to the upper flask oil-hydraulic cylinder, a first back pressure serving as a resistance against an upward movement of the upper flask toward the upper plate during the squeeze process of the lower flask drive unit and the squeeze oil-hydraulic circuit, the first back pressure circuit includes an upper flask free electromagnetic valve configured to free oil flowing to the upper flask cylinder and an upper flask counterbalance valve configured to adjust the pressure of oil freed by the upper flask free electromagnetic valve, and the second oil-hydraulic circuit includes a second back pressure circuit configured to apply, to the lower filling frame oil-hydraulic cylinder, a second back pressure serving as a resistance against a downward movement of the lower filling frame toward the lower plate during the squeeze process of the lower flask drive unit and the squeeze oil-hydraulic circuit, the second back pressure circuit includes an lower filling frame free electromagnetic valve configured to free oil flowing to the lower filling frame oil-hydraulic cylinder and an lower filling frame counterbalance valve configured to adjust the pressure of oil freed by the lower filling frame free electromagnetic valve, wherein the first oil-hydraulic circuit and the second oil-hydraulic circuit adjust the balance between a squeeze force to the upper mold and a squeeze force to the lower mold using the first back pressure and the second back pressure achieved by the upper flask counterbalance valve and the lower filling frame counterbalance valve.