To provide an intake pressure presumption apparatus of an internal combustion engine carrying an evaporative emission purging system in order to accurately presume the pressure of an intake passage without using a pressure sensor.

An intake gas amount GA taken into the intake passage is detected (step 120). A purge amount GPGR which is a flow rate of the purge gas purged into the intake passage is presumed (step 122). Based on an operation status of the internal combustion engine, the maximum intake gas amount GAMAX which is the maximum value of an amount of the intake gas sucked by the internal combustion engine is determined (step 124). It is given that an addition of the intake gas amount GA to the purge amount GPGR is a total intake gas amount. Based on the total intake gas amount GA+GPGR and the maximum intake gas amount GAMAX, a presumed load rate value KLOAD0 is determined (step 126).