Airships are expected to provide new business because of small influence upon the environment and are basically stable in their motion. Pitching oscillation motion with a long period is however easily induced on airships and it is hard to be reduced when their motion is in acceleration by thruster. Such motion is undesirable when airships are used for transporting passengers, and used as the platform for observing low atmosphere and the Earth surface. The pitching motion of airships in acceleration is studied and the problem is formulated mathematically yielding a numerical simulator to study the control problems concerning to the pitching motion of airships.