A wrench with a ratchet device includes a wrench body, a driving set, a cover member and a controlling member. A hole is opened on the wrench body. A receiving space is defined near the hole. An assembling groove is defined near the receiving space. The controlling member is assembled into the receiving space. The driving set has a ratchet and a driving block. The ratchet is assembled into the hole and the driving block is assembled into the receiving space. The driving block abuts against a bottom of the receiving space. The ratchet is engaged with the driving block. The controlling member has a switching member inserted into the assembling groove to move the driving block. Under this arrangement, when the ratchet engages with the driving block, the driving block is stable because the bottom of the receiving space abuts against the driving block.