We have designed and developed an exercise environment to learn logical thinking through activities to assemble logic structures called “Triangle Logic Model.” This model consists of three elements, (1) data, (2) warrant, and (3) claim, corresponding to the simplified Toulmin Model. In the Triangle Logic Model, each of the three elements is placed on its respective corner of a triangle depending on the type of the element. Data, warrant, and claim are placed on the left bottom, right bottom and top corner of a triangle, respectively. The basic design of the exercise based on the model is to require learners to place provided propositions on the corner of a triangle to give the proper role of data, warrant or claim to each of them. Variations of the exercise can be designed by including a few distractors in the provided propositions and/or by previously placing one or two propositions on the triangle. The current stage of this research restricts the content of the logic structure to syllogism and the activities to selecting and assembling provided propositions. Proposed exercise environment realizes automatic answer verification and automatic feedback provision. As an evaluation of this exercise environment, we conducted an experiment with two groups, that is, (1) an experiment group with a pre-test, the exercise using the environment, and a post-test, and (2) a control group with only the pre-and the post-test. The test is the standard test for a national investigation of logical thinking ability by National Institute for Educational Policy Research in Japan. As a result, the average score of the post-test in the experimental group had a statistically significant increase (the effect size was large), whereas there was no significant difference in the control group. Moreover, in the experimental group, there was a statistically significant high correlation between the average time to complete the exercise and the scores of both the pre- and the post-test. In the exercise, because a learner was required to complete a problem to move to the next problem, the correlation suggests that the exercise requests the learner to use their logical thinking ability. These results suggest that this exercise could improve users' logical thinking ability.