A flexible multilayer substrate includes a multilayer body including a plurality of laminated resin layers. The multilayer body includes an innermost surface, which is a surface on an inner side when the substrate is bent, and an outermost surface, which is a surface on an outer side when the substrate is bent. Each of the plurality of resin layers includes a skin layer on one surface. Lamination of the multilayer body includes a skin layer joint plane at one location at a central portion in the thickness direction, and the skin layer and other surface come in contact with each other at another location along the central portion in the thickness direction. A skin layer joint plane is arranged on a side closer to the innermost surface than a central plane in the thickness direction of the multilayer body.