Temperature of microfluidic system is greatly sensitive because of fast heat conduction and small heat capacity due to the scale effect. The purpose of this study is the development of a measurement system for the temperature field of liquids in a microfluidic device with high spatial- and temporal-resolution. Measurement method employed in this study is laser-induced fluorescence using fluorescein with the temperature dependence of fluorescent intensity. In order to measure the transient temperature field, an image-intensified high-speed camera was utilized. The signal-to-noise ratio can be improved by the time- or phase- averaging scheme. Applying the synchronization mechanism, phase-averaged temperature data with the time resolution of $500;{mu}s$ can be obtained. Spatial resolution estimated from the Rayleigh limit was approximately 530 nm. The validity of the developed measurement system was confirmed by the experiments for the transient behavior of the liquid temperature undergoing the laser heating in the microfluidic device.