To easily discriminate whether image data received by a reception part has been acquired by an external trigger or an internal trigger, in order to reduce the load of the reception part.

An image transmission method of transmitting image data by using a high-speed digital transmission bus of a band secured transmission mode has; a partial read step of partially reading image data into a transmission part; an internal and external trigger input step of determining a start point and an end point of partial read of image data in the partial read step; a discrimination step of discriminating an internal or external trigger input; and a step of inputting a flag resulting from discrimination in the discrimination step, to the high-speed digital transmission bus as a part of data.