An angle detection system characterised in that it comprises: a target unit including a reflection target and an encoder pattern showing an angle in a circumferential direction around a central axis of the target unit; and a surveying instrument including a survey unit configured to perform a distance measurement and angle measurement to the reflection target, an encoder pattern reading unit configured to read a bit pattern by acquiring an image including the encoder pattern, cutting out a region of the encoder pattern from the image, and reading pixel rows, a display unit, and an arithmetic control unit, wherein the encoder pattern reading unit includes at least one imaging unit (51,56) changeable in focal length, and the arithmetic control unit includes a distance and angle operation unit configured to calculate a distance and an angle to the reflection target based on the results of distance and angle measurement, an imaging magnification setting unit configured to set an imaging magnification of the imaging unit according to the distance, a cutout range adjusting unit enabling setting of a cutout region of the encoder pattern by using the image displayed on the display unit, an encoder pattern identification determination unit configured to determine whether or not encoder pattern identification is successful by collating the cutout region of the encoder pattern from acquired image with a pattern template of an encoder pattern stored in advance in a storage unit, and perform reading again at an increased imaging magnification when the encoder pattern identification fails, and a read angle operation unit configured to calculate an encoder pattern read angle θ E based on an image of an identified encoder pattern. a target unit including a reflection target and an encoder pattern showing an angle in a circumferential direction around a central axis of the target unit; and a surveying instrument including a survey unit configured to perform a distance measurement and angle measurement to the reflection target, an encoder pattern reading unit configured to read a bit pattern by acquiring an image including the encoder pattern, cutting out a region of the encoder pattern from the image, and reading pixel rows, a display unit, and an arithmetic control unit, wherein the encoder pattern reading unit includes at least one imaging unit (51,56) changeable in focal length, and the arithmetic control unit includes a distance and angle operation unit configured to calculate a distance and an angle to the reflection target based on the results of distance and angle measurement, an imaging magnification setting unit configured to set an imaging magnification of the imaging unit according to the distance, a cutout range adjusting unit enabling setting of a cutout region of the encoder pattern by using the image displayed on the display unit, an encoder pattern identification determination unit configured to determine whether or not encoder pattern identification is successful by collating the cutout region of the encoder pattern from acquired image with a pattern template of an encoder pattern stored in advance in a storage unit, and perform reading again at an increased imaging magnification when the encoder pattern identification fails, and a read angle operation unit configured to calculate an encoder pattern read angle θ E based on an image of an identified encoder pattern.