A piston cooling apparatus (20; 20A; 20B; 20C) to be mounted on an internal combustion engine, comprising: a main body including a communication passage communicating with an oil path formed in the internal combustion engine; a nozzle pipe portion including an oil injection port configured to inject oil having passed through the communication passage toward a piston; and a filter (26; 26A; 26B; 26C) disposed upstream of the nozzle pipe portion in an oil flow passage direction and including a hole having a smaller diameter than the minimum diameter of the oil injection port, the oil being injected toward the piston from the oil injection port, wherein: the main body is mounted on the internal combustion engine in a state where at least a portion of the filter is inserted into the oil path; wherein the filter is removably mounted on an outer surface of an upstream side outer wall portion of the main body, the filter existing upstream of the main body in the oil flow passage direction; and wherein the filter is formed to have a bottomed cylindrical shape including a bottom having the hole at an end of the bottomed cylindrical shape; characterised in that the bottom includes a first surface and a second surface formed in a projecting shape or in a recessed shape in the oil flow passage direction with respect to the first surface; and in that holes are formed in both of the first surface and the second surface. a main body including a communication passage communicating with an oil path formed in the internal combustion engine; a nozzle pipe portion including an oil injection port configured to inject oil having passed through the communication passage toward a piston; and a filter (26; 26A; 26B; 26C) disposed upstream of the nozzle pipe portion in an oil flow passage direction and including a hole having a smaller diameter than the minimum diameter of the oil injection port, the oil being injected toward the piston from the oil injection port, wherein: the main body is mounted on the internal combustion engine in a state where at least a portion of the filter is inserted into the oil path; wherein the filter is removably mounted on an outer surface of an upstream side outer wall portion of the main body, the filter existing upstream of the main body in the oil flow passage direction; and wherein the filter is formed to have a bottomed cylindrical shape including a bottom having the hole at an end of the bottomed cylindrical shape; characterised in that the bottom includes a first surface and a second surface formed in a projecting shape or in a recessed shape in the oil flow passage direction with respect to the first surface; and in that holes are formed in both of the first surface and the second surface. the main body is mounted on the internal combustion engine in a state where at least a portion of the filter is inserted into the oil path; wherein the filter is removably mounted on an outer surface of an upstream side outer wall portion of the main body, the filter existing upstream of the main body in the oil flow passage direction; and wherein the filter is formed to have a bottomed cylindrical shape including a bottom having the hole at an end of the bottomed cylindrical shape; characterised in that the bottom includes a first surface and a second surface formed in a projecting shape or in a recessed shape in the oil flow passage direction with respect to the first surface; and in that holes are formed in both of the first surface and the second surface.