To accurately predict the lifetime of an adapter for supplying a DC power used to be normally connected to a commercial power source.

The adapter for supplying the DC power comprises a power supply unit 1 for converting an AC power into the DC power, and a lifetime deciding unit 2 housed in the same case 3 as the unit 1. In this adapter, the unit 2 has a counting means 11 for detecting the load current and an energizing time of the unit 1, a current and time product calculating means 12 for calculating the product of the load current and the energizing time, a first storage means 13 for updating according to data based on the product of the load current and the energizing time, and a deciding means 15 for deciding the lifetime based on the data of the means 13.