Material flow in Japan as a recycling society has been analyzed. Input resources entering Japanese society is calculated to be 2,050 Mts/y, are potentially recyclable resources for industry is 410 Mts/y, and the maximum amount of recyclable materials is calculated to be 216 Mts/y, taking into account loss by usage. Fundamental equations which describe the material flow in a recycling society and E-r (recycling ratio of materials), E-rr (amplified ratio of recycling), and E-w (reduction ratio of waste materials) should be taken into consideration to decide the construction of a recycling society. Taking steel flow as an example, We studied the present state of recycling, its relationship with harmful substances, the problem of natural and man-made resources and the treatment of "stocks" in material flow. We conclude that there is little chance of constructing the recycling society in Japan if the current mass flow continues in future.