A study on visualization of superheated He II —superheated He I interface in a narrow channel between parallel walls as a result of heating was investigated using a shadowgraph method. It was confirmed that a superheated state was readily created in the narrow channel that simulates cooling channels of superconducting magnets. Superheated He II-superheated He I interface transiently appeared above 2.0 K up to lambda temperature when applying small heat flux. The boiling accompanying with superheated He II- superheated He I interface that was repeatedly generated and collapsed was found to have a high heat transfer coefficient.