Superstring theory, Quantum gravity, Noncommutative field theory The purpose of elementary particle theory is to seek for microscopic structures of matter and to study interactions among elementary particles. Among four fundamental interactions of them the strong, weak and electromagneticones are known to be described as gauge field theories. As for the last one, gravitational interaction is the most well-known force and described classically by general th eory of relativity. But quantum theory of gravity is non-renormalizable and has not b een established yet. The important candidates of the quantum theory of gravity are superstring theo ry and loop quantum gravity. Recently there have been interesting dvelopments in the superstring theory such as Gauge/Gravity duality and noncommuative physics on D branes. In the quantum theory of gravity spacetime may be noncommutative at Plank Scale, because the spacetime itself is a dynamical variable and replaced by an operator upon quantization. I am presently investigating the superstring theory and the noncommuative fiel d theory to clarify these issues of spacetime at short distance.