Mainboard device

The invention discloses a mainboard device which can be assembled and combined with a first M.2 expansion card. The mainboard device comprises a mainboard, a first connector, a supporting frame and a first extension fixing module which penetrates through the supporting frame and is combined with the first M.2 expansion card. The supporting frame is provided with a plurality of supporting spaces. The first connector corresponds to one of the supporting spaces. The first extension fixing module can penetrate through any supporting space and can be clamped in the supporting frame. When the first M.2 expansion card is inserted and combined in the first connector, the first extension fixing module penetrates through the supporting space corresponding to the first connector in cooperation with the length of the first M.2 expansion card, the extension fixing module is combined with the first M.2 expansion card, the first extension fixing module is fixed in the supporting frame, and at the moment, the first M.2 expan