The performance of Stirling engines depends on the performance of regenerators. Regenerators are primarily expected to have good temperature efficiency. In addition, the flow losses and dead space must be minimized. These factors, however, are in opposition to each other.Although a considerable amount of research has focused on these three factors, few studies have analyzed them in actual reciprocating flows. Moreover, it has not been possible to measure the temperature efficiency by using a working gas due to the rapid change of the gas temperature.Therefore, in this study, we measured the transition of the temperature in the reciprocating flows in a regenerator by using water instead of a gas and then examined the characteristics of the regenerator.Here, we report the observed transition of temperature, which almost coincided with results previously obtained by computer simulation.