A solid laser amplification device having a laser medium that has a solid medium, into which a laser light enters and from which the laser light is emitted, and an amplification layer, provided on the surface of the medium, receives the laser light in the medium, and amplifies and reflects the light toward the exit; and a microchannel cooling part that has a plurality of cooling pipelines, into which a cooling solvent is conducted and which are arranged parallel to the surface of the amplification layer, and a cooling surface, at the outer periphery of the cooling pipelines and attached on the surface of the amplification layer, the microchannel cooling part cooling the amplification layer. The closer the position of the cooling pipeline to a position facing a section of the amplification layer that receives the laser light, the greater the cooling force exhibited by the cooling part.