A circuit substrate includes a base and conductive layers disposed on lower and upper surfaces of the substrate. The base includes resin layers and the conductive layers overlapping with each other in a plan view. The resin layers include first resin layers and a second resin layer interposed between the first resin layers. The first resin layer has a filler and the second resin layer has no filler or a filler whose amount is 1 volume % or less and smaller than an amount of the filler in the first resin layer.