One aspect of the present disclosure provides a production method for a composite, the method including: a cooling step of performing cooling under a pressurized condition in a state where a heated molten material of a thermosetting composition is brought into contact with a resin-impregnated body, in which the above-described resin-impregnated body includes a nitride sintered body having a porous structure and a semi-cured product of the thermosetting composition impregnated into the above-described nitride sintered body.