A simple method for the spatial imaging of standing spin-wave modes is demonstrated. We observed instantaneous temperature-rise images on a polycrystalline ferrimagnetic insulator Y3Fe5O 12 slab using an infrared camera immediately after exciting magnetostatic standing spin-wave modes. We found that a wavy temperature distribution appears before the temperature distribution on the sample is smoothed by heat conduction. The distribution is consistent with the result of a calculation based on the Landau-Lifshitz-Gilbert equation using the effective demagnetization coefficient of the slab. This result proves that the method can image the spatially distributed patterns of standing spin waves.