An angle detection device (30, 30A, 30B), comprising: a plurality of photoemitters; a plurality of photodetectors each forming a linear light-receiving area, the plurality of the photodetectors being configured with CMOS image sensors, the photodetectors being paired to the photoemitters respectively; a scale plate disposed between the plurality of photoemitters and the plurality of photodetectors; and a control section (33, 33A, 33B) that controls the plurality of the photoemitters and the plurality of the photodetectors; wherein the control section (33, 33A, 33B) includes fewer analog-front-ends (43, 43A) than the plurality of the photodetectors, the analog-front-end (43, 43A) converting analog signals (Ia) sent from each of the plurality of the photodetectors into digital signals (Id), an arithmetic processor that detects a rotating posture of the scale plate based on the converted digital signals (Id), and a signal switch (42, 42A) that selectively connects one of the plurality of the photodetectors to the analog-front-end, wherein the analog-front-end (43, 43A) does not have a memory to temporarily store the analog signals and the digital signals, and wherein the control section simultaneously emits lights from the plurality of the photoemitters, simultaneously receives the emitted lights by the corresponding photodetectors respectively, and executes data processing of: sending a switching signal to the signal switch (42, 42A) to switch the photodetector to be connected for outputting the analog signals (Ia), sending an output signal to each photodetector separately, outputting the analog signals (Ia) simultaneously acquired by the photodetectors and representing an entire area of the light-receiving area of one of the plurality of the photodetectors to the analog-front-end, converting the outputted analog signals (Ia) into the digital signals (Id) with the analog-front-end, and outputting the converted digital signals (Id) to the arithmetic processor, for each of the plurality of the photodetectors one by one in sequence. a plurality of photoemitters; a plurality of photodetectors each forming a linear light-receiving area, the plurality of the photodetectors being configured with CMOS image sensors, the photodetectors being paired to the photoemitters respectively; a scale plate disposed between the plurality of photoemitters and the plurality of photodetectors; and a control section (33, 33A, 33B) that controls the plurality of the photoemitters and the plurality of the photodetectors; wherein the control section (33, 33A, 33B) includes fewer analog-front-ends (43, 43A) than the plurality of the photodetectors, the analog-front-end (43, 43A) converting analog signals (Ia) sent from each of the plurality of the photodetectors into digital signals (Id), an arithmetic processor that detects a rotating posture of the scale plate based on the converted digital signals (Id), and a signal switch (42, 42A) that selectively connects one of the plurality of the photodetectors to the analog-front-end, wherein the analog-front-end (43, 43A) does not have a memory to temporarily store the analog signals and the digital signals, and wherein the control section simultaneously emits lights from the plurality of the photoemitters, simultaneously receives the emitted lights by the corresponding photodetectors respectively, and executes data processing of: sending a switching signal to the signal switch (42, 42A) to switch the photodetector to be connected for outputting the analog signals (Ia), sending an output signal to each photodetector separately, outputting the analog signals (Ia) simultaneously acquired by the photodetectors and representing an entire area of the light-receiving area of one of the plurality of the photodetectors to the analog-front-end, converting the outputted analog signals (Ia) into the digital signals (Id) with the analog-front-end, and outputting the converted digital signals (Id) to the arithmetic processor, for each of the plurality of the photodetectors one by one in sequence. sending a switching signal to the signal switch (42, 42A) to switch the photodetector to be connected for outputting the analog signals (Ia), sending an output signal to each photodetector separately, outputting the analog signals (Ia) simultaneously acquired by the photodetectors and representing an entire area of the light-receiving area of one of the plurality of the photodetectors to the analog-front-end, converting the outputted analog signals (Ia) into the digital signals (Id) with the analog-front-end, and outputting the converted digital signals (Id) to the arithmetic processor, for each of the plurality of the photodetectors one by one in sequence.