Judging from the general condition of its coal reserve in quantity and quality, the best of the coal reserve in the Ishikari coal field lies in the northern part of Sorachi district and the southern part of Yubari district. The second best lies in the north of Yubari district (Ikushunbetsu area). In comparison with these areas, the north eastern (most of Ashibetsu area) and the southern Sorachi and middle Yubari are inferior to the other areas both in quantity and quality of the coal reserve. Four big companies, that is, Mitsui Mining Co., Ltd., Mitsubishi Mining Co., Ltd., Sumitomo Coal Mining Co., Ltd., Hokkaido Colliery and Steamship Co., Ltd. have monopolized most of resources in this coal field, particulary almost all of superior mines.
The structure of coal production in this coal field was founded on the base of this monopolization of resources. Its features in 1957 are as follows.
1. Big collieries (with over 100, 000tons of the annual product), the number of which was only a quarter of all collieries, monopolized 88 per cent of the total amount of production.
2. Above mentioned four big companies monopolized in fact 84 per cent of the total production.
3. Many small collieries were located in the mining areas possessed and paid rent for their operation by these big comanies.
Since 1958, as the internatinal petrolium companies have penetrated into the Japanese energy market, the coal mining industry in Japan has got a hard damage and been forced to rationalize its way of production and management under the support of the Japanese Government. In the Ishikari coal field, most of small collieries disappeared in the second period of rationalization (1962-1965). While, a number of big collieries have survived, though some of them were closed. In this case, most of the “scrapped” collieries were located in inferior locational conditions and most of the “built” collieries were located in the superior areas. Hence the poor coal seams were abandoned and only the better ones survived. And a part of the existing collieries have been separated from the direct management of big companies and put under the control of another companies (“Dainigaisha”) which have been completely controled in fact by these big companies. Another part of the existing collieries have separated the inferior mining areas and made another companies to manage them, or abandoned them perfectly, and cocentrated on the exploitation of superior coal seams.
As a result of these rationalization, the structure of the coal production in the Ishikari coal field in 1970 has much changed in comparison with that in 1957. The points of this change are as follows.
1. The monopolization of production by big collieries has been strengthened (88-93 per cent).
2. The monopolization of production by big companies including the production by “Dainigaisha” has been also strengthened (84-97 per cent).
3. Almost all of small collieres which had located in the mining areas possessed by big companies disappeared.
