A holding device includes a base, an upper holding arm unit connected to an upper portion of the base, and a pair of lower holding arm units connected to the base. Each of the lower holding arm units includes a lower holding arm that is connected to the base and that is rotatable between upper and lower positions. Each lower holding arm is movable relative to the base in a sliding direction between an extended position and a contracted position. Each of the lower holding arm units further includes a stop member that extends into the base and that is operable for positioning the lower holding arm relative to the base. The lower holding arm units cooperate with the upper holding arm unit to define a holding space for retaining a display.