A two-dimensional absolute position sensor comprises at least one magnetic slit thin plate provided to an end-effector which is attached to the end of a robot arm and moves in a plane, and having slits extending in the X and Y directions, magnetic sensor heads having magnetic sensors for position measurement in the X and Y directions opposed to the magnetic slit thin plate through a gap therebetween and bias magnets for applying magnetic fields to the magnetic sensors, and a signal processing circuit for outputting an absolute position signal generated from signals outputted from the magnetic sensors. Therefore, a small-sized, light-weighted two-dimensional absolute position sensor with an excellent environment-resistance used for readily measuring the two-dimensional absolute position of the end-effector of a robot in a non-contact manner can be provided.