A hot-rolled copper plate consists of pure copper having a purity of 99.99 mass % or greater, the hot-rolled copper plate having an average crystal grain diameter of 40 μm or less, and a (Σ3+Σ9) grain boundary length ratio (L (σ3+σ9)/L), which is a ratio between a total crystal grain boundary length L measured by an EBSD method and a sum L (σ3+σ9) of a Σ3 grain boundary length Lσ3 and a Σ9 grain boundary length Lσ9, being 28% or greater.