The present study aims at analyzing the mechanism of increasing mobihty related to work-trips in the Tokyo Metropolitan Region. In the previous paper, the author analyzed three qualitative characteristics of the increase in work-trips by applying "Integrated Population Density". The purpose of this paper is statistical analysis and model building of the increase in work-trips. The conclusions are as follows: 1) The following characteristics are clarified by the statistical analysis of each municipality. a) The increase in population is in stable proportion to the increase in workers by residential place. b) The ratio of minimum employment, that increases in proportion to the increase in the popula-tion, to the population becomes large when the degree of integrated population density goes up. c) The ratio of the increase in the in-commuter to the increase in employment becomes large when the degree of integrated population density goes up. Therefore, the increase in commuters in a municipality can be estimated precisely by using the model of the change in population components. 2) There are many previous studies about work-trips in urban areas. But the spread effect, the sub-ject of this study, is the indirect effect. Therefore there are difficulties in applying the thus previous studies for this effect. In this paper, the model for estimating the spread effect in the increase in work-trips in created by the idea of the diffusion on an order measured by the integrated population density. In this model, the increase in work-trips of every municipality becomes the endogenous variables. The model can be used to estimate the spread effect. Then the mechanism of the in-crease in work-trips, analyzed in the previous paper, is described quantatively.