The utility model discloses a drill bit size detection device of a drilling device. The device comprises a support base and a detection body. wherein a detection main body is fixed above the supporting base; a first dial gauge is mounted at the upper end of the detection main body; a second dial gauge and a third dial gauge are mounted at the edge of the front side of the detection main body; thesecond dial gauge and the third dial gauge are respectively provided with a second measuring rod and a third measuring rod; The second dial indicator, the third dial indicator and the first dial indicator are all provided with digital display screens. A first measuring head is fixed to the front end of the second measuring rod, a second measuring head is fixed to the front end of the first measuring rod, a third measuring head is fixed to the front end of the third measuring rod, the second dial gauge and the third dial gauge are both connected with the detection body through a fixing base, and a limiting sleeve is arranged on the second measuring rod. The drill bit size detection device of the drilling device is simple in structure, convenient to use and capable of accurately detecting the diameter and the length of the drill bit.