It is said that humans have unknown power known as ki (bio-psychokinesis). Ki is also not unlike other forms of bio-energy, such as prana in ancient India or psi in modern parapsychology. Referred also as energy medicine, spiritual healing and prayer therapy, these practices have been executed throughout different points in history and countries all over the world. Moreover, energy medicine has been used in hospitals recently. However, there are many unresolved problems with such bio-energy. The focus of this book is the author's biophysical study on anomalous phenomena, which are claimed to be caused by bio-energy. In Chapter I, the author describes the concept of ki in modern Japan. He also describes the concept of bio-sensors to detect implicit anomalous weak energy. Bio-sensors are important in modern parapsychology, and many successful studies are done using bio-sensors. In Chapter II, the author summarizes new findings obtained through his studies by using the pieces of a cucumber. Through his unique methods, various properties of ki (psi) are found. The most important finding is that the ki (psi) phenomenon follows simple laws in physics. The author measured the spatial distribution of ki-field, which is generated around a human body. The result of the world's first quantitative measurement of ki-field is shown in this book. In Chapters III & IV, the author explains the detail of how to use cucumbers as a bio-sensor for weak bio-energy; some examples of these are gas, biophoton, and fluorescence measurement methods. The author describes them for students and beginner studiers of ki (psi), and the readers will be able to understand and execute them by themselves completely. A brief touch on Japanese studies on ki (psi) is shown in Chapter V. Additionally, the author describes Chinese parapsychological study. These historic inheritances will help the readers to understand research senses of the modern study on ki and psi.