A circuit board includes a board body, a card slot, a release structure, and a transmission mechanism. The card slot is disposed on the board body and adapted for inserting an expansion card. The release structure is rotatably disposed beside the card slot. The transmission mechanism includes a contact part and a stressed part that are linked to each other, wherein the contact part is connected to the release structure. When the stressed part receives an external force, the contact part is moved correspondingly, so that the release structure is rotated relative to the card slot, thereby releasing the expansion card.