An apparatus for preparation of an emulsion, comprising - a heating device with a plunger pump, diaphragm pump, or cylinder pump, into which water flows continuously or intermittently to obtain heated and pressurized water or a water-insoluble substance to be emulsified flows continuously or intermittently to obtain a heated and pressurized water-insoluble substance; - a first flow merger comprising multiple liquid supply ports and a single liquid outlet, in which under pressure, the heated and pressurized water obtained by the heating device continuously or intermittently merges with a water-insoluble substance to be emulsified or the heated and pressurized water-insoluble substance to be emulsified obtained by the heating device continuously or intermittently merges with water; - a mixing apparatus having an outlet, into which the water and the water-insoluble substance, merged by the first flow merger, flow, and the water-insoluble substance is dissolved in the water while being maintained at a temperature and pressure in the vicinity of the vapor-liquid critical point of water, being temperature and pressure conditions that are below the critical temperature and/or critical pressure at which water does not exhibit a supercritical state and at which water and the water-insoluble substance are miscible; - a second flow merger in which the water-insoluble substance dissolved in water flowing out from the mixing apparatus merges with a surfactant at a temperature and pressure in the vicinity of the vapor-liquid critical point of water, being temperature and pressure conditions that are below the critical temperature and/or critical pressure at which water does not exhibit a supercritical state and at which water and the water-insoluble substance are miscible; - a cooling device into which the liquids merged by the second flow merger flows and a mixture of the dissolved material and surfactant is cooled to obtain an emulsion in which the water-insoluble substance is emulsified in water or an emulsion in which water is emulsified in the water-insoluble substance; and - a pressure valve; and wherein the heating device, the first flow merger, the mixing apparatus, the second flow merger, the cooling device and the pressure valve are connected to each other in the order → → → → cooling device → pressure valve. - a heating device with a plunger pump, diaphragm pump, or cylinder pump, into which water flows continuously or intermittently to obtain heated and pressurized water or a water-insoluble substance to be emulsified flows continuously or intermittently to obtain a heated and pressurized water-insoluble substance; - a first flow merger comprising multiple liquid supply ports and a single liquid outlet, in which under pressure, the heated and pressurized water obtained by the heating device continuously or intermittently merges with a water-insoluble substance to be emulsified or the heated and pressurized water-insoluble substance to be emulsified obtained by the heating device continuously or intermittently merges with water; - a mixing apparatus having an outlet, into which the water and the water-insoluble substance, merged by the first flow merger, flow, and the water-insoluble substance is dissolved in the water while being maintained at a temperature and pressure in the vicinity of the vapor-liquid critical point of water, being temperature and pressure conditions that are below the critical temperature and/or critical pressure at which water does not exhibit a supercritical state and at which water and the water-insoluble substance are miscible; - a second flow merger in which the water-insoluble substance dissolved in water flowing out from the mixing apparatus merges with a surfactant at a temperature and pressure in the vicinity of the vapor-liquid critical point of water, being temperature and pressure conditions that are below the critical temperature and/or critical pressure at which water does not exhibit a supercritical state and at which water and the water-insoluble substance are miscible; - a cooling device into which the liquids merged by the second flow merger flows and a mixture of the dissolved material and surfactant is cooled to obtain an emulsion in which the water-insoluble substance is emulsified in water or an emulsion in which water is emulsified in the water-insoluble substance; and - a pressure valve; and