To set an appropriate knock determination value without being affected by change in vibration intensity distribution due to frequent occurrences of knocks or system variations, in a knock determination device for an internal combustion engine.

In a system, a vibration intensity lvpk is determined from an output signal of a knock sensor, and a knock determination value vkdl (=vmed+usgm_L) is determined by adding a value of u times the lower side standard variation sgm_L to a median vmed of a vibration intensity distribution, then it detects presence or absence of a knock is determined by comparing the vibration intensity lvpk with the knock determination value vkdl. A distribution state of the vibration intensity distribution is determined, based on an upper standard deviation sgm_H and the lower standard deviation sgm_L of the vibration intensity distribution, and a knock detection frequency is determined, based on the number of times that is determined as presence of knock for each predetermined number of times of ignitions. Then, the knock determination value vkdl is corrected so that the knock detection frequency falls within an appropriate range by correcting u value, based on the distribution state of the vibration intensity distribution and knock detection frequency.