The detent means for a heat sink has on each of the two ends of a pressing member a fixing engaging member and a movable engaging member, the movable engaging member is provided thereon with a foldable member. Wherein the pressing member is provided on the heat sink, the fixing engaging member extending downwards to engage protrusions on a side of a fixing seat of a microprocessor, the movable engaging member can be lowered to engage with protrusions on an opposite side of the fixing seat of the microprocessor, and the movable engaging member can be raised to a predetermined level under the action of the foldable member to thereby exert a force on the pressing member, thus the heat sink and the microprocessor at the center of the fixing seat can be press connected with each other.