An engine fuel injection control device whereby appropriate engine output is obtained without generation of smoke, by determining a smoke limit fuel injection amount, using an inferred air intake amount when the engine operating condition is in a transient state etc. An inferred air intake amount calculation device (42) calculates an inferred air intake amount by using the target fuel injection amount on the previous occasion and the engine rotational speed. If the air amount deviation between the inferred air intake amount and the detected air intake amount detected by a mass airflow sensor (34) is more than a prescribed value, the detected air intake amount is deemed to be subject to detection lag. Then, the inferred air intake amount is selected as the final air intake amount, and the final fuel injection amount is calculated in accordance with this final air intake amount.