An assistance-limit recognizing device for recognizing a limit of assistance made by a vacuum booster that is configured to assist an operating force applied to a brake operating member. A communication between a variable pressure chamber and a negative pressure chamber of the vacuum booster is established, when the operating force is not applied to the brake operating member. A communication between the variable pressure chamber and the atmosphere is established while the communication between the variable pressure chamber and the negative pressure chamber is cut off, when the operating force is applied to the brake operating member, whereby the operating force applied to the brake operating member is assisted based on a pressure difference between a pressure in the negative pressure chamber and a pressure in the variable pressure chamber. The assistance-limit recognizing device is configured, upon reduction of the variable-pressure chamber pressure in process of change of the variable-pressure chamber pressure toward the atmospheric pressure with application of the operating force to the brake operating member, to recognize the limit of the assistance made by the vacuum booster.