1. An automatic collimation device for a surveying apparatus comprising: an imaging device that images a target captured by a telescope and surroundings of the target; a drive unit that rotates the telescope; a light emitting unit that sends light toward the target; and an arithmetic control unit that determines a position of the target based on a difference between a lit image obtained as a result of imaging by the imaging device when the light emitting unit has been turned on and an unlit image obtained as a result of imaging by the imaging device when the light emitting unit has been turned off and controls the drive unit to automatically collimate the target, wherein the arithmetic control unit carries out a correlation operation between the lit image and unlit image so as to determine a position where both images are most coincident, and determines a position of the target based on a difference between both images at the position.