Originally, this line served the coal traffic between Saitozaki and the over 50 collieries south of the city of Fukuoka around Shime and Umi. Saitozaki is a peninsula opposite Fukuoka across the Bay of Hakata and is situated at the western end of a long, slim sand dune that stretches up to the northeast and the town of Wajiro. The northern section of the Kashii-sen from Kashii Junction on the Kagoshima Honsen to Saitozaki is 12, 9 km long; Kashii lies slightly to the northeast of the city of Fukuoka, 3, 7 km south of Wajiro. Much of the Kashii - Saitozaki line is through the sand dunes known as Umi-no-Nakamichi ("The road through the sea").
The southern section of the Kashii-sen is 12, 5 km long and runs from Kashii into the hills that were once the site of very intensive coal mining. Two railways and a number of branches for coal trains served this region. The railway to the west was the Katsuta-sen (13, 8 km long), passing by the large colliery at Shime and closed in 1985, the railway to the east is the present-day southern section of the Kashii-sen. All collieries closed in the mid-1960s, and railway services into the region became very run-down. Like the Katsuta-sen, the Kashii-sen also appeared doomed, but as the city of Fukuoka began to spread into the former coalmining area and new industries and settlements developed there the line has been spared.
In the north across Hakata Bay, the sand dune area around Umi-no-Nakamichi once had been a naval base and military airport and then became an important US military base. After being returned to Japanese use in 1972 development as a resort commenced. Saitozaki has become the centre of a residential area with new housing as well as modern high-rise apartments. Afforestation of the sand dunes is rapidly turning the area into an attractive pine forest. Apart from the Kashii-sen, which needs to make its way around the bay, two ferries link Saitozaki to the city of Fukuoka, of which Saitozaki became a suburb in 1971.
The Kashii-sen was built in 1904/5; it became part of the State Railway system in 1944. All freight trains ceased by the mid-1980s. Today the line sees two to three through stopping diesel trains per hour.
