A magnetic marker diagnostic system configured to diagnose operation situations of magnetic markers laid as spaced in or on a traveling road so as to be magnetically detectable by a vehicle, the diagnostic system comprising: a magnetic measuring part configured to obtain a one-dimensional or two-dimensional magnetic distribution by measuring a magnitude of magnetism with which any of magnetic markers acts therearound, wherein the magnetic measuring part includes magnetic sensors (Cn) and a data generation circuit, wherein the data generation circuit is configured to generate magnetic distribution data indicating a magnetic distribution of magnetic measurement values in a vehicle-width direction by the magnetic sensors (Cn); the magnetic marker diagnosis system being characterised in that it further includes an imaging part configured to obtain a marker image, which is one-dimensional or two-dimensional image information including the vehicle-width direction, by imaging the magnetic marker; and a diagnosing part configured to determine presence or absence of a flaw in the magnetic marker based on a comparison between the magnetic distribution and the marker image; wherein the diagnosing part has a threshold processing part which performs a threshold process regarding a positional deviation between a distribution center in the magnetic distribution and a center of a marker area in the marker image, and is configured to determine presence or absence of the flaw in accordance with the result of the threshold process, or wherein the diagnosing part is configured to obtain an index indicating symmetry of the marker image or the marker area with reference to a distribution center in the magnetic distribution and determine presence or absence of the flaw by a threshold process regarding the index. a magnetic measuring part configured to obtain a one-dimensional or two-dimensional magnetic distribution by measuring a magnitude of magnetism with which any of magnetic markers acts therearound, wherein the magnetic measuring part includes magnetic sensors (Cn) and a data generation circuit, wherein the data generation circuit is configured to generate magnetic distribution data indicating a magnetic distribution of magnetic measurement values in a vehicle-width direction by the magnetic sensors (Cn); the magnetic marker diagnosis system being characterised in that it further includes an imaging part configured to obtain a marker image, which is one-dimensional or two-dimensional image information including the vehicle-width direction, by imaging the magnetic marker; and a diagnosing part configured to determine presence or absence of a flaw in the magnetic marker based on a comparison between the magnetic distribution and the marker image; wherein the diagnosing part has a threshold processing part which performs a threshold process regarding a positional deviation between a distribution center in the magnetic distribution and a center of a marker area in the marker image, and is configured to determine presence or absence of the flaw in accordance with the result of the threshold process, or wherein the diagnosing part is configured to obtain an index indicating symmetry of the marker image or the marker area with reference to a distribution center in the magnetic distribution and determine presence or absence of the flaw by a threshold process regarding the index.