To obtain the irradiation magnetic field distribution of each channel of a multichannel transmission RF coil at high speed, for multiple channels which are all or some of the channels of the transmission coil, an image is acquired by irradiation with one channel or a combination of two or more channels, an irradiation magnetic field distribution upon irradiation with all of the multiple channels is acquired, and the irradiation magnetic field distribution of each channel is calculated using the acquired irradiation magnetic field distribution of all of the multiple channels and the phase difference calculated from the image of each channel and the image of all of the multiple channels.
