There is provided a metal thin film comprising a metal plate and a diamond particle dispersed in the metal plate. According to the present invention, the metal thin film has a film thickness of 5 nm to 35000 nm. The diamond particle is dispersed almost homogeneously over the direction of the film thickness of the metal thin film. The metal thin film has the diamond particle at a concentration of 1 to 12%. According to the present invention, based on conversion into an equivalent circle, the diamond particle has a first particle size distribution with respect to a first particle of a first particle size of 16 nm or less, at a first number average existence rate of 50% or more; the diamond particle has a second particle size distribution with respect to a second particle having a second particle size of 50 nm or more, at a second number average existence rate of substantially 0%; and the diamond particle has a third particle size distribution with respect to a third particle having a third particle size of 2 nm or less, at a third number average existence rate of substantially 0%.