A position sensing device for mobile robots comprises a light-receiving element configured such that light is focused on different positions of the light-receiving element according to the distance from an obstruction, a light-emitting element to emit the light, which is reflected by the obstruction and is incident on the light-receiving element, in a straight line, the light-emitting element serving to emit the light at a predetermined angle to the external jamming light such that an imaginary obstruction formed by an external jamming light incident on the light-receiving element is positioned out of an effective sensing range, a signal processing unit to calculate the distance from the obstruction based on the position where the light incident on the light-receiving element is focused, and an incorrect signal processing unit to determine whether the obstruction is present within the distance considering the change of the distance sensed by the position sensing device while the mobile robot is driven. Consequently, the mobile robot is properly operated although the external jamming light is present, and incorrect recognition of the distance from the obstruction due to reflection of the light, which is emitted while being inclined, not by the obstruction but by a floor of a moving space is prevented.