A method of determining a quality of a cladding layer according to one aspect of the present invention is a method of determining a quality of a cladding layer 16 formed by irradiating a laser beam 30 while a metallic powder 26 is being supplied, the method including: a process of capturing an image of a melt pool 31 and an area around thereof while the cladding layer 16 is being formed; a process of measuring the sizes and the number of ball-shaped metallic powder aggregates absorbed in the melt pool 31 from the image that has been captured; and a process of determining the quality of the cladding layer 16 based on the sizes and the number that have been measured.