The temperature T dependence of the mechanical resonance frequency f r of longitudinal sound waves in sintered bulk samples of Bi 2Sr 2CaCu 2O 8+δ has been measured from room temperature down to liquid-nitrogen temperature. The f r increases steeply around 200 K with decreasing T and on the other hand it decreases steeply around 230 K with increasing T. This hysteresis of f r has a width depending on the change rate of T. Keeping T at a point T f between 230 K and 200 K, the time dependence of f r has been measured. The f r increases toward a saturated value f r max on the hysteresis loop determined by T f. When the time t is scaled by a characteristic time t 1 2 when f r reaches the middle point between the initial and the saturated ones, the plots of f r/ f r max versus t/t 1 2 at each T f are almost reduced to one universal curve independent of T f. These results suggest that the sample experiences a first-order phase transformation around those temperatures.