A magnetometer includes a diamond sensor, an excitation light source, a diamond sensor case, and a photodiode. The excitation light source irradiates the diamond sensor case with excitation light. In the diamond sensor case, a reflection film which reflects excitation light is formed on either a front surface or an inner surface, and the diamond sensor is stored. The photodiode detects intensity of fluorescence generated from the diamond sensor. The diamond sensor case includes a fluorescence output window and an excitation-light reception window. Fluorescence generated by the diamond sensor is output through the fluorescence output window. Excitation light emitted by the excitation light source is received through the excitation-light reception window. The photodiode is provided on a side of a second surface opposite to a first surface which is a magnetism measurement surface of the diamond sensor.
