A system of measurement for the thermal diffusivity of porous materials was developed. Although there are several measurement systems for thermal diffusivity, it is typically difficult to measure the thermal diffusivity of porous materials. This paper presents a measurement system for thermal diffusivity that utilizes a cyclic heating method along with the verification of the measured device. To verify the cyclic heating method, the available reference data of aceramic specimen was utilized. To apply the system to an actual porous material, polystyrene foam was tested. The thermal diffusivity of the polystyrene foam under vacuum was reduced by 63%. The measured values from both tests were in good agreement with the reference values, as they were within 10% of these values.