Bamboo-shaped carbon nanotubes fabricated by the catalytic growth method with Ni/metallic oxide catalyst are systematically studied using transmission electron microscopy. It is found that except for the nodes the bamboo-shaped carbon nanotubes can be regarded as stacking of truncated conical graphene sheets. Depending on the size of a catalyst, the Ni particles can be encapsulated inside the tubes or at the growth front of the tubes with a plug-shape. A linear relationship between size of the nanotube and the catalyst particle is found. The results suggest that the nanometer-sized Ni catalyst particles are in the liquid state during nanotube growth. A simple model for the growth of bamboo-shaped nanotubes is proposed.