In this paper, I considered about comprehension strategies instruction on reading of expository texts with a focus on conditional knowledge. First, I set up three critical conditions as follow, (1) goal of reading, (2) text, and (3) task. These conditions influence the use of conditional knowledge. Second, I theoretically considered the conditional knowledge instruction with a focus on "explicit instruction" "setting of two different types of context" "collaboration with others". As a result, I clarified that learning of conditional knowledge is facilitated when students read expository text in "multiple context" after they read "similar context". Finally, I considered two lesson practices which are conscious to conditional knowledge instruction as follow, (1) the lesson practice by Myke Rock which is picked up by Janice F. Almasi and Susan King Fullerton (2012), (2) the lesson practice by Yoshinori Takao which is picked up Seiji Tsuruda (2010). Through these considerations, I made the theory of conditional knowledge instruction specific as teaching and learning process.