An operating method of an image sensing device capable of detecting several light emitting diodes each having a flickering cycle time, the image sensing device includes several pixel circuits, each of the several pixel circuits includes a first sensing circuit and a second sensing circuit, the operating method including the following operations: operating the image sensing device in a first operating mode, including: sensing light by the first sensing circuit with a first exposure time longer than the flickering cycle time, thereby obtaining a first sensing result; sensing light, simultaneously by the first sensing circuit and the second sensing circuit with a second exposure time shorter than the flickering cycle time, thereby obtaining a second sensing result and a third sensing result; determining whether there is LED (light emitting diode) flickering or not according to the first sensing result, the second sensing result and the third sensing result.