This paper proposes a general synthesis framework to attenuate disturbance responses which are caused due to switching. The objective function to be minimized is the worst-case L₂ gain from the past disturbance to the future output. The problem formulation is given in a general manner so that controller switching is a special case. In particular, this paper assumes that some of state variables before switching can be exactly available and also that some of those after switching can be manipulated without affecting control output directly. Necessary and sufficient conditions for synthesis are given in terms of LMIs. It follows that solutions can be obtained efficiently. Moreover, this paper shows that reduced order compensators exist under the above assumptions.