This invention provides a vapor heat apparatus for treating fruits by killing insects such as, for example, a Mediterranean fruit fly, an orange small fruit fly, a Queensland fruit fly and a melon fruit fly or the like. The invention prevents thermal troubles experienced by fruits undergoing treatment by allowing each of the fruits stored in each of the fruit storing means to reach a predetermined fruit central temperature at substantially the same time. The vapor supplying means and the heat exchanger means are controlled in reference to a sensed signal of the fruit temperature sensing means. When the increase in the fruit central temperature in a certain fruit storing unit is delayed as compared with the increase of the central temperature of the fruits in another fruit storing unit, the relative humidity of the saturated vapor passing in the former fruit storing units is increased increasing thermal conductivity or a feeding amount of the saturated vapor passing in the former fruit storing unit is increased increasing the amount of heat provided to the fruit and increasing the thermal conductivity is to hasten the rise in the fruit central temperature.