The disclosure provides a wear warning device including a caliper, two brake pads, an elastic component and a first switch. The caliper has two push parts. The two push parts are respectively disposed at a first wall surface and a second wall surface of the caliper. The brake pads are located between the two push parts. The elastic component includes two arm parts and a connection part located between the arm parts. The arm parts are respectively disposed on the brake pads. The first switch is located between the arm parts. When the brake pads are in a worn-out state and the push parts are moved toward each other to force the brake pads to clamp a brake disk and to force the two arm parts to move toward each other, one of the arm parts activates the first switch to produce a wear warning signal.