A battery holder mechanism for holding a battery in an electronic device having a package has a battery holder body adapted to be received in a receiving hole of the package. The battery holder body has a circular-arc portion extending along the circumferential direction of the battery. First and second supporting projection project from the inner peripheral edges of the circular-arc portion and support the battery from both sides. A supporting projecting portion disposed in the package within the receiving hole at a position corresponding to a circumferential interval between the second supporting projection so as to support the battery from the same side as the second supporting projection when the battery holder body is inserted in the battery receiving hole. Engagement pauls resiliently lock the battery holder body within the battery receiving hole. The battery is held by the projections from both sides, so the vertical displacement of the battery can be restricted.