This invention reliably returns a measurement surface to a reference position while weakening the elastic force of a spring. A tool length measurement apparatus of this invention includes a supporter that supports the measurement surface that the tip of a tool contacts while translating in accordance with a biasing force received from the tool. The tool length measurement apparatus of this invention also includes a detector that detects the position of the measurement surface in a translation direction. The tool length measurement apparatus of this invention also includes a biasing unit that biases the measurement surface by a gas in a direction against the biasing force received from the tool.