Environmental education is educational activities using nature. Since the importance of environmental education is increasing, development of effective leaders training methods and learning programs is required. We consider that by using learner’s interests during educational activities for learning evaluation, we can improve the teaching methods of instructors and learning programs. In this research, we use gaze directions to measure interests. In outdoor such as environmental education, it is difficult to apply gaze estimation techniques using conventional cameras due to the effects of sunlight and fog. In addition, since the wearable device imposes a physical burden on the learner, it has a problem that natural state data cannot be measured. we attach a compact and lightweight device to a cap or helmet. In this research, we measure head direction and estimate gaze direction from the data. The head direction measurement system uses a transmitter with three ultrasonic speakers and receiver. We can measure horizontal and vertical head direction by received time difference of ultrasound transmitted from three speakers. By using the M-sequence for the transmission wave, the spectral efficiency increases, enabling simultaneous measurement of the head direction by many people. In the experiment, we measured horizontal head direction using two ultrasonic speakers. In the result, it was possible to identify the M-sequence and received time. The error in the head direction was 5 degrees.