A sensor to measure the intensity of power flux on the surface of food during microwave heating has been constructed, and measurements of the power flux intensity incident from the top surface of a cylindrical container were performed using the newly constructed sensor. The container was filled with water, and the power flux estimated from the temperature increase of the water after heating was confirmed to agree with the power flux measured using the sensor. Therefore, the ability of the sensor to measure the intensity of the incident power flux was confirmed. Next, the distribution of power flux intensity was measured in the radial direction for the cases of microwaves incident at the top surface, bottom surface, and top and bottom surfaces of the cylindrical container, respectively. This distribution of power flux intensity varies greatly depending on the heating conditions, but the temperature in the interior of food calculated using this value agreed almosts with the observation results using a liquid crystal sheet.