The present invention is to provide a device for activating a substance, which is a flexible sheet that is available regardless of the shape of each of the device that has a substance to be activated inside. The member for activating a substance 1 of the present invention is flexible. The member for activating a substance 1 includes a metal layer 11 containing a metal with a redox potential of 0 V or less or an alloy of a metal with a redox potential of 0 V or less and a radiation generating layer 12 containing a mixture of a natural ore containing a radioactive substance with a radiolucent resin. The dose of radiation generated from the radiation generating layer 12 is from 0.02 μSv/h or more to 0.2 μSv/h or less. To enhance the flexibility, a radiation shielding layer that shields radiation generated from the radiation generating layer 12 is preferably unformed.