A light emitting diode (LED) tube lamp includes: a lamp tube, for receiving an external driving signal, a rectifying circuit, a filtering circuit, and an LED module coupled to the filtering circuit and configured to receive a filtered signal for emitting light, wherein the LED module comprises an LED unit, a current-limiting element for receiving the external driving signal, the current-limiting element coupled to one or more of the external connection terminals, and coupled to or in the rectifying circuit, and a ballast interface circuit coupled to the current-limiting element and having a first terminal and a second terminal, for the LED tube lamp to be compatible with a ballast providing the external driving signal, wherein the ballast interface circuit comprises a detection circuit and a switching circuit coupled to the detection circuit, and the ballast interface circuit is configured to detect whether the external driving signal comes from a ballast, and to conduct or cut off the switching circuit based on a result of the detection. The detection circuit is configured such that, when the external driving signal is from a ballast and is being input to the LED tube lamp, the detection circuit conducts the switching circuit according to a state of a property of a detection signal transmitted through the first terminal and the second terminal.