To provide an anti-runout device for tool with a simple independent structure easily mountable on a device frame, securing an enough processing stroke while preventing a runout of a long tool.

This device comprises a holder, a guide bar, a tool holding means, a slide bar, an adjust holder and a spring as basic components for being an independent type anti-runout device for tool with integrated structure having each component serially arranged collinearly to be capable of being mounted easily on a frame of processing device. Also since the tool holding means initialized in stroke nearly to a center of a long tool can move forward corresponding to a forward movement of the processing device after moving the processing device for a predetermined distance, an enough deep hole processing stroke can be obtained.