A ball screw device includes an elongated shaft having an outer groove, a ball nut having a screw hole for receiving the elongated shaft and having a passage communicating with the screw hole of the ball nut, and a lubricating device includes an inner cylindrical element engaged onto the elongated shaft and secured to the ball nut, a housing attached onto the cylindrical element and contacted with the ball nut, and the housing includes a chamber for receiving a lubricating grease, an oil distributing member is engaged into the passage of the ball nut and engaged into the screw hole of the ball nut for engaging with the elongated shaft, and an inner element is engaged in the housing and engaged with the distributing member for supplying the lubricating grease to the distributing member.