Explanation can be viewed as a task of making a hearer understand the contents of an explanation produced by an explainer. This requires the explainer to take into consideration the cognitive load which the hearer will bear in understanding the explanation. Current explanation technology has focussed on reducing the load. This load reduction contributes to facilitating the hearer's understanding. However, this approach often fails to reinforce his/her understanding. Another approach to explanation is to apply a load to a hearer's understanding process. Such a load application leads the hearer to pay more attention to his/her understanding process because he/she finds it more challenging to try a heavier load. Moreover, a hearer may reach impasses due to the applied load more often than not. However, the supporting explanations for the impasses may promote the understanding process. This paper describes a load application framework, which brings these effects of the load application, and its evaluation. In the framework, understanding an explanation is regarded as building up a knowledge structure by relating the contents of the explanation to already retained knowledge. In addition, the cognitive load is represented as the amount of knowledge-structuring processes. This framework provides the following load application manner. The knowledge structure,which a hearer will finally build up, is first set up. Second an explanation is presented to the hearer. In understanding this explanation. he/she will bear the load of recollecting his/her related knowledge (recollection load) and complementing the knowledge structure by combining the given explanation with his/her knowledge (complement load). This paper also describes an experiment with the load application framework. The main purpose of this experiment is to ascertain whether the knowledge-structuring with a load is more effective for retaining the information a hearer acquires than that with no load. As a result of the experiment, we ascertained that the load application reinforced the retention. In addition, we found out the following three factors Contributing to the retention : (1) the different effect of recollection load and complement load, (2) load heaviness effect. (3) impasse effect.