An air compressor device includes a cylinder housing and a supporting plate. The air compressor further comprises a piston engaged in the cylinder housing and having a piston rod, a gear and an eccentric member attached to the supporting plate with a shaft. The eccentric member includes an eccentric pin coupled to the piston rod. A motor includes a protrusion engaged into an orifice of the supporting plate, with a spindle extended out of the protrusion and extended through the orifice of the supporting plate. The motor further includes a pinion attached to the spindle and engaged with the gear. The pinion includes an outer diameter greater than an outer diameter of the protrusion of the motor.