An apparatus and method for automatically supplying insulin based on exercise amount are provided. The apparatus includes a blood sugar measurer for measuring a blood sugar level of a patient; a controller for, comparing the measured blood sugar level with a predetermined blood sugar level, if the measured blood sugar level is greater than or equal to the predetermined blood sugar level, determining whether a current time is within a blood sugar change time zone, if the measured blood sugar level is equal to or higher than the predetermined blood sugar level, and if the current time does is not within the blood sugar change time zone, acquiring exercise amount information about the patient and determining a dose of insulin to be injected inject into the patient based on the acquired exercise amount information, if the current time does not fall within the blood sugar change time zone; and an insulin injector for injecting the determined dose of insulin into the patient.