We report an experimental study on a transient spatial pattern formation of a cholesteric liquid crystal, cholesteryl oleyl carbonate, induced by rapid temperature change. The spatial pattern like a network is found to be induced when the temperature is increased faster than a constant rate of 0.5 mK/s. We have measured the optical transmittance of the liquid crystal continuously during the pattern formation process and have found that the component corresponding to the network clearly appears in addition to the selective reflection of the helical structure. The observed spatial pattern is discussed in relation to the spectral shape of the transmittance.