There is provided an MRI apparatus capable of measuring the B1 distribution of an RF transmission coil in a short time with high accuracy. In order to realize this, imaging means of the MRI apparatus includes a B1 distribution measurement sequence that includes an application of a pre-pulse by RF radiation means and a plurality of signal acquisition sequences with different elapsed time (TI) from the pre-pulse. The signal acquisition sequence uses a pulse having a small flip angle as an RF pulse and is executed before the longitudinal relaxation after the pre-pulse ends. Calculation means calculates the B1 distribution of the RF radiation means using image data with different TI acquired in the respective signal acquisition sequences.