[Problem]This invention aims at solving the problem of how a subscriber premises-side optical network unit can be switched to an evaluation mode without the use of a jig board.[Means for Solving the Problem]The invention refers to a subscriber premises-side optical network unit (ONU 10) which is connected to a center-side optical network unit (OLT 1a) via an optical transmission line (optical fiber 2, 4) and to an external device (switch 6) via an electric signal line (electric signal line 5); comprising a memory (memory switch 15a) the stored content of which can be directly or indirectly rewritten by the external device; a detection part (CPU 15) for detecting that the content of the memory has been rewritten; and a control part (CPU 15) for performing, when the detection part detects that the stored content of the memory has been rewritten, a control whereby the optical sending part which sends optical signals to the optical transmission line is put into a continuous light emission state.