I conducted educational research on investigation activities adopting performance tasks. The task set in lessons was “To Measure Pentane Vapor Pressure.” For the purpose of completing the task, the fundamental knowledge and concepts of the course unit, “Gaseous Properties”, should be used comprehensively. Attainment targets were clarified by showing the students an evaluation index which included the objectives of the activities and essential points of the experiment. These activities were found to be effective in the students’ acquisition of fundamental knowledge and concepts. The activities also helped the students to consider how they should relate the fragments of information they obtained from the experiments and how clearly they should show the essential parts. The investigation activities were evaluated based on the evaluation index.