Experimental and analytical investigations were conducted to identify the frequency response characteristics of a beam system with a minute clearance at the support. A beam in the shape of the letter L was adopted as the system, which made it possible to compare the results of the two investigations easily by restricting the direction of vibration at the clearance. The frequency response characteristics of the systems were evaluated in terms of the equivalent linearization method using the describing function approach. The jump phenomena around the natural frequency and the suppression of the compliance around the natural frequency could be evaluated by the analytical method; the results agreed well with those obtained by experiment. The computation time needed for the proposed method was significantly shorter than that needed by a numerical integration approach, the approach most commonly used in conventional design practice. The method also made it possible to evaluate the response characteristics in detail in terms of compliance.