In a movie we usually happen to watch such a scene that large T.rex chases human. In "Jurassic Park", people riding on a car had a narrow escape from T.rex. It implies that T.rex could run faster than human, then people should ride on a car. However, T.rex has been thought as a slow runner in the field of paleontology since 2002 when a theory is published that stated on limited capacity of locomotion ability of T.rex . This book is intended to answer the question, namely, T.rex was a fast runner or not. This book is composed of two parts. Basic biomechanics of the musculoskeletal is described in the first half of this book. Over 150 references on muscle kinematics are introduced in this part, which is a rich introduction to a reader who want to study animal locomotion. In the latter half of this book the author presents the result of detailed calculation on the possibility of fast running of T.rex.