A method and apparatus for measuring the particle diameter of foam on a malt alcoholic drink, which can detennine the quality of the foam of the malt alcoholic drink objectively, are provided. The apparatus for measuring the particle diameter of foam on a malt alcoholic drink according to the present invention includes a laser light source for irradiating a linear laser beam onto the surface of a foam layer created on a malt alcoholic drink, an imaging device for imaging a laser line reflected on the surface of the foam layer to obtain an image of the laser line, and a calculating device for obtaining edge information of the laser line from the image of the laser line to calculate the particle diameter of foam in the foam layer based on the edge information.