To provide a signal output unit and a manuscript reader for detecting whether there is disorder in one of a pre-stage output unit or a post-stage output unit in a simple constitution at low cost.

A signal output unit 35 including a photoelectric conversion element (image sensor) 21 for reading a manuscript optically and converting to an electric signal and a signal output device (A/D converter) 33 for processing the electric signal from the photoelectric element 21 and generating a digital signal in parallel is provided. A process inhibiting unit for inhibiting the process of the signal output device 33 is provided, and the process of the signal output device 33 is prohibited by an operation of the process inhibiting unit at the start of test. In addition, a test pattern generating element 39 for blocking the output of each digital signal from signal output device 33 and generating a test signal having a prescribed pattern (for example, Hi, Low patterns alternately) for each signal line 61 to 79 of the signal output device 33 is provided.

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