Panel member

A panel member comprising

• a plurality of circular or elliptical recessed parts linearly arranged, wherein:
• when it is assumed that a portion where three recessed parts are linearly aligned is called a recessed part group, there are at least a first recessed part group and a second recessed part group arranged in parallel with the first recessed part group;
• an angle formed between a first straight line linking a center of the recessed part in the first recessed part group and a center of the recessed part in the second recessed part group located at a position closest to the recessed part in the first recessed part, and, a second straight line linking centers of the recessed parts in the first recessed part group is 80 degrees or more and 100 degrees or less;
• the recessed part is composed of a bottom part constituting a bottom surface of the recessed part and a side wall part erected around the bottom part;
• and
• an inclination angle ξ formed between the bottom part and the side wall part is 20 degrees or more and 90 degrees or less.