The aim of this paper is to find out the general tendencies of public administrative services (PAS) and per capita annual expenditures (PCAE) in relation to the population size and area on the basis of the latest data in Japan, thereby to show the optimum size of a city, to evaluate the efficiency of actual PAS and PCAE, and to estimate the effects on PAS and PCAE of the annexation of municipalities. The main results are as follows.
① When we select the population size and area as explanatory variables, PAS, PCAE and PAS/PCAE can be explained significantly with the level of significance 0.01.
② The optimum size of a city is a population of 210~270 thousand inhabitants in view of PCAE, and 240~300 thousand inhabitants in view of PAS/PCAE. On the other hand, we can not show the optimum size in view of PAS, because the lager the population size is, the higher the PAS is.
③ In our cases, the optimum size of a city does not depend on the value of area when we have population size and area as explanatory variables.
④ On the basis of above results, we can evaluate the efficiency of actual PAS and PCAE, and to estimate the effects on PAS and PCAE of the annexation of municipalities.