An electronic apparatus includes an input device and an illumination device. The illumination device includes a chassis, an illumination module and a positioning mechanism. The module is pivotally connected to the chassis to be rotatable between a closed and an open position. The positioning mechanism is use for respectively positioning the illumination module in the closed and the open position. An operating method of the illumination device includes the following steps. First, a push force is applied to the module in the closed position. Then the module rotates from the closed position to the open position. The module enters a light-on state as arrived in the open position for illuminating the input device. Next, another push force is applied to the module in the open position, so that the module rotates to the closed position. The module enters a light-off state as arrived in the closed position.