A pedestal assembly (20) includes a chassis (200), a gear wheel (300) pivotably mounted to the chassis, two supporting members (400) coupled to the chassis, and a coil spring (500) received between the chassis and the gear wheel. The chassis includes a stop portion (222) depending downwardly from a side of a top wall (210) thereof. The gear wheel includes first teeth (330) extending from a periphery thereof. Each supporting member includes a rack (440) comprises second teeth (444) engaging with the first teeth, and a first clasping portion (448) formed on an outer side thereof. When one of the first clasping portions is locked by the stop portion, the coil spring is compressed, while when the first clasping portion is unlocked from the stop portion, the coil spring is decompressed and drives the gear wheel to rotate to cause the supporting members to move relative to the gear wheel.