A polymerization apparatus, comprising: a light irradiator; and a polymerization vessel, the polymerization apparatus being for polymerizing an unpolymerized portion formed of a photopolymerization curable composition by applying light emitted from the light irradiator to an object that includes a member or an article having the unpolymerized portion housed inside the polymerization vessel, wherein the light irradiator includes a first casing that includes a light source chamber defined by cylindrical side walls, a ceiling, and a floor including a light-transmissive window member, an intake hole and an exhaust hole being provided on the side walls, a light source assembly that includes a base having a light-emitting surface on which a plurality of light-emitting diodes is disposed in a predetermined pattern and a heat-dissipating surface to which a heat sink is joined, the heat sink further including a plurality of heat-dissipating fins disposed in parallel at predetermined intervals to form a groove-like air passage between the heat-dissipating fins adjacent to each other, the light source assembly being disposed within the light source chamber so that the light-emitting surface faces the light-transmissive window member, an intake fan disposed within the light source chamber so as to face the intake hole and one end of the air passage, and an exhaust fan disposed within the light source chamber so as to face the exhaust hole and the other end of the air passage, the polymerization vessel includes a polymerization cup that has a frustoconical or substantially frustoconical shape that opens upward and increases in diameter upward, and is capable of housing an object therein, and a second casing that is a bottomed cylindrical or box-shaped casing having an opening at an apex thereof, the polymerization cup being attachably/detachably housed in the second casing via the opening, and light that has been emitted by the plurality of light-emitting diodes of the light irradiator and has passed through the light-transmissive window member is applied to the inside of the polymerization cup of the polymerization vessel. a light irradiator; and a polymerization vessel, the polymerization apparatus being for polymerizing an unpolymerized portion formed of a photopolymerization curable composition by applying light emitted from the light irradiator to an object that includes a member or an article having the unpolymerized portion housed inside the polymerization vessel, wherein the light irradiator includes a first casing that includes a light source chamber defined by cylindrical side walls, a ceiling, and a floor including a light-transmissive window member, an intake hole and an exhaust hole being provided on the side walls, a light source assembly that includes a base having a light-emitting surface on which a plurality of light-emitting diodes is disposed in a predetermined pattern and a heat-dissipating surface to which a heat sink is joined, the heat sink further including a plurality of heat-dissipating fins disposed in parallel at predetermined intervals to form a groove-like air passage between the heat-dissipating fins adjacent to each other, the light source assembly being disposed within the light source chamber so that the light-emitting surface faces the light-transmissive window member, an intake fan disposed within the light source chamber so as to face the intake hole and one end of the air passage, and an exhaust fan disposed within the light source chamber so as to face the exhaust hole and the other end of the air passage, a first casing that includes a light source chamber defined by cylindrical side walls, a ceiling, and a floor including a light-transmissive window member, an intake hole and an exhaust hole being provided on the side walls, a light source assembly that includes a base having a light-emitting surface on which a plurality of light-emitting diodes is disposed in a predetermined pattern and a heat-dissipating surface to which a heat sink is joined, the heat sink further including a plurality of heat-dissipating fins disposed in parallel at predetermined intervals to form a groove-like air passage between the heat-dissipating fins adjacent to each other, the light source assembly being disposed within the light source chamber so that the light-emitting surface faces the light-transmissive window member, an intake fan disposed within the light source chamber so as to face the intake hole and one end of the air passage, and an exhaust fan disposed within the light source chamber so as to face the exhaust hole and the other end of the air passage, the polymerization vessel includes a polymerization cup that has a frustoconical or substantially frustoconical shape that opens upward and increases in diameter upward, and is capable of housing an object therein, and a second casing that is a bottomed cylindrical or box-shaped casing having an opening at an apex thereof, the polymerization cup being attachably/detachably housed in the second casing via the opening, and a polymerization cup that has a frustoconical or substantially frustoconical shape that opens upward and increases in diameter upward, and is capable of housing an object therein, and a second casing that is a bottomed cylindrical or box-shaped casing having an opening at an apex thereof, the polymerization cup being attachably/detachably housed in the second casing via the opening, and light that has been emitted by the plurality of light-emitting diodes of the light irradiator and has passed through the light-transmissive window member is applied to the inside of the polymerization cup of the polymerization vessel.