In recent years, catheter-based interventional diagnosis and therapy have become increasingly popular. However, the operation of the catheter requires certain human skill because conventional catheters can not bend actively for steering. For the bending motion, we have developed active catheters which has many joints of Shape Memory Alloy (SMA) coil actuators in order to move like a snake. Polymer link active catheter which has link structures between the joints, and linkless type active catheters which have no joint were developed. Linkless outskeletal active catheters which have SMA coils inside the linter coil were also developed. This is suitable for practical use in a human body because of its small heat dissipation from the surface.