A tool calibration apparatus for a robot manipulator having a tool is disclosed. The tool calibration apparatus comprises a base, an X-axis measurement device, a Y-axis measurement device and a Z-axis measurement device. Each of the X-axis measurement device, the Y-axis measurement device and the Z-axis measurement device comprises a measuring plate and a sensor. The measuring plates of the X-axis measurement device, the Y-axis measurement device and the Z-axis measurement device move in a direction along the X-axis, Y-axis, and Z-axis, respectively. The sensors of the X-axis measurement device, the Y-axis measurement device and the Z-axis measurement device measure a displacement of the corresponding measuring plate. According to the displacements, information of a tool center point of the tool is acquired so as to calibrate the tool center point.