Numerical analysis of heat and fluid flow in a thermoacoustic device has been performed to clarify the effect of thermal conditions to be set on the temperature change of a stack. Transient one-dimensional equations of continuity, momentum and energy were solved utilizing a TVD scheme. A miniature thermoacoustic oscillator of standing wave type was used as the physical model. The physical model has a simple structure and comprises a cylindrical pipe closed on one end side and opened on the other side and a stack of honeycomb structured ceramic compact disposed therein. When the end of the stack on the closed end side is heated, self-excited oscillation occurs and the temperature of the stack increases. The behaviors of temperature change of the stack were analyzed while individually varying the value of the thermal conditions and compared with each other and with the experimental one. As a result, the influences of the thermal conditions on the temperature change of the stack were clearly showed. The result of this research provides a clue when setting thermal conditions in numerical analysis.