A heat sink fastening device is used for facilitating fixing a heat sink on a circuit board. The heat sink fastening device includes a first connecting portion, a second connecting portion and at least a connecting member. The first connecting portion is included in the circuit board. The second connecting portion is included in the heat sink. The connecting member is disposed on a first surface of the circuit board and includes a first connecting part and a second connecting part. The first connecting part is coupled to the first connecting portion of the circuit board and the second connecting part is coupled to the second connecting portion of the heat sink, thereby facilitating fixing the heat sink on the first surface of the circuit board.