In this note, we extend our previous result on robust stability analysis for linear time-invariant parameter-dependent (LTIPD) systems to stability analysis for linear parameter-varying (LPV) systems in which parameters are possibly time-varying, and propose a design method of gain-scheduled (GS) state-feedback controllers using the proposed stability analysis method. Multiple slack variables (SVs) are used to derive our analysis and synthesis methods. Conservatism of our methods decreases as the sizes of SVs, i.e. the numerical complexity, are increased. Simple numerical examples borrowed from the literature demonstrate the effectiveness of our proposed design method.