Provided are a magnetic marker and a magnetic marker detection system with a reduced magnetic force. The magnetic marker detection system (1S) in which magnetism generated from the magnetic marker (1) laid on a road surface (53) is detected by a magnetic sensor (2) attached to a vehicle's body floor (50) of a vehicle (5) is a system with the magnetic marker (1) and the magnetic sensor (2) in combination, the magnetic marker having a magnetism reach ratio Gh/Gs, which is a ratio of a magnetic flux density Gh at a position at a height of 250 mm with respect to a magnetic flux density Gs of a surface, being equal to or larger than 0.5% and the magnetic sensor using a magneto-impedance element including a magneto-sensitive body with impedance changing in accordance with an external magnetic field.