An object of the present invention relates to a thermosetting adhesive sheet that, without the use of a metal reinforcement sheet, which is regarded as a major factor responsible for an increase in thickness of electronic devices and other devices, reinforces a flexible printed circuit to such a level that detachment of mounted components, for example, is prevented, prevents warping, and has good electrical conductivity. The present invention relates to a thermosetting adhesive sheet configured to be used to reinforce a flexible printed circuit. The thermosetting adhesive sheet includes a woven fabric, a nonwoven fabric, or a metal base of 50 μm or less thickness and a thermosetting adhesive layer adjacent to at least one surface of the woven fabric, the nonwoven fabric, or the metal base of 50 μm or less thickness.