A flashlight includes a battery housing, a lamp seat, a lamp unit, a heat-conductive casing, and a heat-dissipating plate. The lamp seat is mounted on one end of the battery housing. The lamp unit includes a substrate having a first side provided with a metal layer, and an LED lamp mounted on a second side of the substrate opposite to the metal layer. The heat-conductive casing is attached to the battery housing, and is disposed around the lamp seat and the lamp unit. The heat-dissipating plate is sandwiched between the lamp seat and the metal layer of the substrate, and is in contact with the heat-conductive casing. Heat generated by the lamp unit is dissipated via the metal layer, the heat-dissipating plate, and the heat-conductive casing.