In Kaluza-Klein theory,') gauge fields are known to be unified into the gravitational field in a higher-dimensional spacetime with a compact extra space. If one makes the metric on the higher-dimensional spacetime reduce to the metric on the four-dimensional spacetime and compact extra space by means of the dimensional reduction, one can get the usual action for the gauge and gravitational fields from Einstein action in the higher-dimensional spacetime. Associated with such a dimensional reduction, it is necessary to fix the scale of extra space at the order of Planck length in order to realize the usual coupling constant of gauge fields and gravitational field. Within the framework of the classical theory, however, it is known that Kaluza-Klein metric is unstable as a higher dimensional gravity.2) In quantum theory, there arises another approach to the theory of gravity, that is, induced gravity.3) In that theory, the spacetime metric is obtained as collective coordinates of quantized matter fields. The Kaluza-Klein theory, then, can be derived from matter fields defined in the 4-dim. spacetime with a compact extra space. The equation of motion for the metric in induced gravity coincides with the usual one in Einstein theory within the approximation disregarding the higher order terms of inverse Planck mass. 4