A fluorescent LED illumination device fittable between a pair of sockets already provided for a fluorescent lamp, comprising a first power supply circuit that illuminates LED's by using a DC power obtained by converting and rectifying an AC power supplied from the sockets, and a second power supply circuit that illuminates the LED's by using an internal battery, characterised in that said fluorescent LED illumination device comprises a controller (14, 21) configured to discriminate one of: a normal lighting mode (S103, S105), wherein the LED's are lightened via said first power supply circuit or said second power supply circuit when a light switch is ON; a normal light-out mode, wherein the LED's are not lightened when said light switch is OFF; and an emergency lighting mode, wherein the LED's are lightened as emergency lights via said second power supply circuit when an AC power supply is not alive, said controller further configured to operate, in response to a result of said discrimination, to select an applicable one among said normal lighting mode, said normal light-out mode and said emergency lighting mode, said controller configured to detect a change, within a predetermined time interval, of a voltage or current value of electricity flowing into the illumination device to discriminate such that: if, within the predetermined time interval, said value is lowered only one time from a predetermined value of electricity that will normally flow when the light switch is ON to substantially zero, and which remains at substantially zero, a power failure is determined to have interrupted the AC power supply, and the controller is configured to control the illumination device such that the normal lighting mode is switched to the emergency lighting mode, whereas, if, within the predetermined time interval, there occurs a change of the current or voltage value including a decrease from the predetermined value of electricity that will normally flow when the light switch is ON to substantially zero, followed by an increase to said predetermined value, the normal light-out operation is determined to have been carried out, and the controller is configured to control the illumination device such that the normal lighting mode is switched to the normal light-out mode. if, within the predetermined time interval, said value is lowered only one time from a predetermined value of electricity that will normally flow when the light switch is ON to substantially zero, and which remains at substantially zero, a power failure is determined to have interrupted the AC power supply, and the controller is configured to control the illumination device such that the normal lighting mode is switched to the emergency lighting mode, whereas, if, within the predetermined time interval, there occurs a change of the current or voltage value including a decrease from the predetermined value of electricity that will normally flow when the light switch is ON to substantially zero, followed by an increase to said predetermined value, the normal light-out operation is determined to have been carried out, and the controller is configured to control the illumination device such that the normal lighting mode is switched to the normal light-out mode.