A technique of approximate measurement by the space reflection method is described for the surface impedance of a planar electromagnetic wave absorber backed by a conducting plate and a dipole array-type frequencyselective surface among the microwave devices exhibiting a single-tuned reflection. The frequency characteristics of the complex scattering matrix S 11 are measured for commercially available 3-GHz rubberized ferrite and nonwoven cloth absorbers in the case of the former and for four types of dipole arrays at 3, 10, and 13 GHz forming conducting reflector made of copper sheets on Styrofoam in the case of the latter. From the measured results, the surface impedance is calculated. It is found that agreement is fairly good for the object to be measured that satisfies the derivation condition for the theory. From the result, the applicable range of the measurement method is shown for a single-tuned reflection-type general microwave device for which the surface impedance cannot easily be calculated theoretically. In addition, it is found that the method is effective for design of microwave equipment made of a device with such reflection characteristics to which other devices are attached.