A solid laser amplification device comprising: a laser medium part which has a solid medium , configured to be entered by a laser light (L) from an entrance part on a side surface of the solid medium , to let the laser light (L) travel through the laser medium part and to emit the laser light (L) from an exit part on a side opposite to the entrance part to the outside, and an amplification layer which is respectively provided on a lower bottom surface and an upper bottom surface of the solid medium , is configured to receive the laser light (L) in the solid medium , and to amplify and reflect the laser light (L) toward the exit part ; and a microchannel type cooling part which has a microchannel part which is a plate-shaped member extending in horizontal directions X and Z and having a thickness extending in a vertical direction Y, the plate-shaped member having a plurality of cooling pipes , through which a cooling solvent (W) can pass and which are arranged in a direction parallel to a surface of the amplification layer , and a cooling surface which is a surface of the microchannel part and is mounted on the surface of the amplification layer , and is configured to cool the amplification layer , wherein each of the plurality of cooling pipes (36Ab,36Bb36Cb,36Db,36Eb) has an inlet pipe , the inlet pipe is connected to a first pipe extending in a direction approaching the cooling surface , and a second pipe which is connected to the first pipe and extends in a direction away from the cooling surface , and an outlet pipe , which outlet pipe is connected to the second pipe , through which the cooling solvent (W) from the inlet pipe to the outlet pipe can flow, so that the cooling of the amplification layer is performed by the cooling solvent (W) of the first pipe and the second pipe , which can flow in the first direction Y perpendicular to the cooling surface , rather than the cooling solvent (W) flowing in the second direction Z parallel to the cooling surface . a laser medium part which has a solid medium , configured to be entered by a laser light (L) from an entrance part on a side surface of the solid medium , to let the laser light (L) travel through the laser medium part and to emit the laser light (L) from an exit part on a side opposite to the entrance part to the outside, and an amplification layer which is respectively provided on a lower bottom surface and an upper bottom surface of the solid medium , is configured to receive the laser light (L) in the solid medium , and to amplify and reflect the laser light (L) toward the exit part ; and a microchannel type cooling part which has a microchannel part which is a plate-shaped member extending in horizontal directions X and Z and having a thickness extending in a vertical direction Y, the plate-shaped member having a plurality of cooling pipes , through which a cooling solvent (W) can pass and which are arranged in a direction parallel to a surface of the amplification layer , and a cooling surface which is a surface of the microchannel part and is mounted on the surface of the amplification layer , and is configured to cool the amplification layer , wherein each of the plurality of cooling pipes (36Ab,36Bb36Cb,36Db,36Eb) has an inlet pipe , the inlet pipe is connected to a first pipe extending in a direction approaching the cooling surface , and a second pipe which is connected to the first pipe and extends in a direction away from the cooling surface , and an outlet pipe , which outlet pipe is connected to the second pipe , through which the cooling solvent (W) from the inlet pipe to the outlet pipe can flow, so that the cooling of the amplification layer is performed by the cooling solvent (W) of the first pipe and the second pipe , which can flow in the first direction Y perpendicular to the cooling surface , rather than the cooling solvent (W) flowing in the second direction Z parallel to the cooling surface . <EOS>