The present invention provides an activating agent of stem cells and/or progenitor cells comprising a thrombin-like enzyme which can be used in regenerative medicine, and particularly in regenerative medicine utilizing self-regeneration, acting promptly and moderately depending on the state of advancement and the degree of injured organs and/or tissues to which regenerative medicine is applied, with few or no side effects. The present invention also provides a method for activating stem cells and/or progenitor cells in an animal comprising the step of administering to the animal an effective amount of a thrombin-like enzyme and use of the thrombin-like enzyme for activating stem cells and/or progenitor cells.