A portable automatic syringe device having a configuration including a separable rotating shaft adapted to provide a drive force to a piston included in the automatic syringe device so that the rotating shaft can be separated, along with the piston, from a housing of the syringe device upon re-filling a syringe of the syringe device with a liquid medicine. A coupling member is coupled between the rotating shaft and power transmission means. The coupling member has a reduction gear engaging with an output gear of the power transmission means, and a cross groove. A horizontal engaging pin is fixed to a lower end of the rotating shaft in such a fashion that it is engaged in the cross groove when the rotating shaft is positioned in position in the syringe device, thereby causing the rotating shaft to be coupled to the coupling member. An injection needle unit is also provided which includes an "L" shaped injection needle member provided with a curved portion capable of absorbing impact, thereby preventing a breakage of the injection needle member. The injection needle unit also includes a sensor for sensing an abnormal blood sugar level generated due to an abnormal injection of a liquid medicine.