I. Introduction
Since early times, the control problem of the system with input delay has been investigated by many researchers (see, e.g., the monograph [9] and references therein). The sphere of the control objects treated in [9] ranges from lumped parameter systems to distributed parameter systems, and from linear systems to nonlinear systems. Especially, when one considers the thermal control problem, large time lag exists in the feedback loop, since it is generally difficult to regulate heat quickly. So, it is very important to study the control problem of parabolic systems with input delay.