We propose a simple structure for manipulating resonant conditions in random structures, which is composed of a waveguide structure as a defect region embedded in a random structure. Using the two-dimensional finite-difference time-domain method, we examine the resonant properties of localized modes bound in the waveguide. From the results, we confirm that long-lived modes are strongly confined in the waveguide only when the resonant frequency matches the frequency windows in the transmitted intensity spectrum of the surrounding random structure.