A terahertz image measurement device (10) is provided with a terahertz detection sensor (13), a magnetic field generating unit (19), and a measurement control unit (20). The sensor (13) detects near-field light of terahertz light emitted from a sample (18). The magnetic field generating unit (19) has a coil (19a) disposed around the sample (18) and the sensor (13), the coil (19a) being wound so as to surround the optical axis of terahertz light irradiated on the sensor (13) from the sample (18), and applies to the sensor (13) a magnetic field generated by allowing an electric current to flow through the coil (19a). The measurement control unit (20) allows an electric current to flow through the coil (19a), changes a value of the electric current to set a strength of the magnetic field to a magnetic field value for which a detection signal level of the terahertz light of the sample detected by the sensor (13) increases prominently, and allows the magnetic field value to conform to a specific frequency of the t
