An elevating device comprises a base, a support on the base, an elastic telescopic module on the support, and an adapter connected with the elastic telescopic module. The elastic telescopic module comprises a first frame body with a first accommodating space therein for positioning a first constant-force spring, and a second frame body with a second accommodating space therein for positioning a second constant-force spring. The second frame body has an top end located beneath the first frame body's bottom end, the first constant-force spring has one end passing out of the first accommodating space and fixed onto the bottom end of the second frame body, while the second constant-force spring has one end passing out of the second accommodating space and fixed onto the top end of the first frame body, so that the first and second frame body are moved in a reverse direction.