An optical line monitoring apparatus (10A, 10B) comprising: first measurement means (15, 16, 15B) for propagating first monitor light through an optical line (32, 33n), receiving first reflected light occurring when the first monitor light propagates, and acquiring a reflectance distribution along a light propagation direction in the optical line (32, 33n) as a first measurement result by OTDR or OCDR; second measurement means (15, 15B) for propagating second monitor light through the optical line (32, 33n), receiving second reflected light occurring when the second monitor light propagates, and acquiring a reflectance distribution along the light propagation direction in the optical line (32, 33n)as a second measurement result by OCDR; and a control section for causing the first measurement means (15, 16, 15B) to acquire the first measurement result with a first spatial resolution and then causing the second measurement means to acquire the second measurement result in the range of a portion of the optical line (32, 33n), which is determined according to the first measurement result, with a second spatial resolution smaller than the first spatial resolution, wherein the control section is adapted to determine a position of a discrete reflection point in the optical line according to the second measurement result, to obtain a degree of contribution of reflection at the discrete reflection point due to the first measurement result according to the determined position of the discrete reflection point and the first spatial resolution by a convolution operation of the first measurement result with the discrete reflection part, to correct the first measurement result according to the obtained degree of contribution, and to output the corrected result. first measurement means (15, 16, 15B) for propagating first monitor light through an optical line (32, 33n), receiving first reflected light occurring when the first monitor light propagates, and acquiring a reflectance distribution along a light propagation direction in the optical line (32, 33n) as a first measurement result by OTDR or OCDR; second measurement means (15, 15B) for propagating second monitor light through the optical line (32, 33n), receiving second reflected light occurring when the second monitor light propagates, and acquiring a reflectance distribution along the light propagation direction in the optical line (32, 33n)as a second measurement result by OCDR; and a control section for causing the first measurement means (15, 16, 15B) to acquire the first measurement result with a first spatial resolution and then causing the second measurement means to acquire the second measurement result in the range of a portion of the optical line (32, 33n), which is determined according to the first measurement result, with a second spatial resolution smaller than the first spatial resolution, wherein the control section is adapted to determine a position of a discrete reflection point in the optical line according to the second measurement result, to obtain a degree of contribution of reflection at the discrete reflection point due to the first measurement result according to the determined position of the discrete reflection point and the first spatial resolution by a convolution operation of the first measurement result with the discrete reflection part, to correct the first measurement result according to the obtained degree of contribution, and to output the corrected result.