An arm exercising device includes a frame, a linkage mechanism, and an impeding unit disposed to apply a resistance force to the linkage mechanism. The frame includes an upright support that has a fixed guide rod. The linkage mechanism includes a pair of swing arms pivotally mounted on the upright support for swinging upward and downward, a runner sleeve disposed slidably over the guide rod for movement upward or downward, a pair of linking rods, each connected between the runner sleeve and one of the swing arms, and a force transmitting cord connected to the handgrips and the swing arms. The resistance force applied to each arm of the user who grips both handgrips and pulls downward is applied evenly to enable a smooth exercise to be performed.