Boiling heat transport characteristics of pressurized (1atm) He II in a vertically placed rectangular cross-sectional channel have been experimentally and analytically investigated. A wire heater is attached at the midpoint of the channel. The temperature distribution of helium in the bottom closed channel is almost the same as that in the bottom opened channel when the boiling occurs. It is considered from the present results that almost all of the input heat is removed by a natural convection when the boiling occurs and low temperature helium is supplied mainly from the top of the channel. When the heat generation ceases, the temperature of the heater in the bottom opened channel recovers to the He II bath temperature faster than that in the bottom closed channel. The time for the recovery does not depend on He II bath temperature for the case of the bottom opened channel.