A simple structural model explaining the gravity and magnetic anomalies was proposed along 2 profiles across the Pacific coast of the eastern Hokkaido (from Kushiro to Nemuro Peninsula). Recently, gravity and magnetic anomaly maps of offshore of this area were published. This area is characterized by high gravity and high magnetic anomalies. From the distribution of Nemuro formation, it was difficult to account for the source of highly positive gravity anomaly belt along the Nemuro Peninsula. Dolerites which compose a part of Nemuro formation were collected in this area. These samples have high density, susceptibility and strong NRM. Curie temperatures and Verwey transition indicate that magnetic carrier is mainly magnetite. Our 2-D modeling referred to these rock density and magnetic data. The result of it revealed that (1) the high gravity anomaly belt along Nemuro Peninsula was attributed to shallow dolerite bodies, and (2) high magnetic anomaly belts of offshore Kushiro was presumably caused by serpentinite.