A hand-muscle developer, comprising a tubular base having a rocker arm pivotably connected thereto at one end by a pair of connecting plates and a pair of links with two pairs of torsional springs respectively retained therebetween. Operator's hand is inserted through the tubular base to hold a cross bar on the rocker arm and to drive it to rotate back and forth. Rotating the tubular base causes the torsional springs to produce a resisting force against the applied force from operator's hand and therefore, operator's hand muscles are trained. Adjusting screws are provided for adjusting the tension of the torsional springs.