A regenerator includes a casing including a connection channel for making a high temperature part and a cooling part communicate with each other; and a thermal energy storage material inserted in the connection channel of the casing and made of an aramid fiber which stores/radiates heat of a working fluid flowing through the connection channel. A cryocooler includes the regenerator. Accordingly, regeneration performance of storing heat included in the working fluid and transmitting the stored heat to a working fluid is improved, and simultaneously a weight is decreased, thereby minimizing abrasion of components.