To provide a pressure intensifying apparatus for compressed fluid which is relatively small in size, inexpensive and energy-saving.

The intensifying apparatus is provided with a pressure intensifying cylinder 17 wherein a cylinder 18 is divided into a plurality of cylinder rooms 23a, 23b into which pistons 19a, 19b connected together by means of a piston rod 20 are respectively inserted, and a plurality of inlet ports 25a, 25b for introducing the compression fluid into respective cylinder rooms and an outlet port 27 for discharging the fluid from the cylinder room 23b located at outermost end of the cylinder are provided. When compressed fluid of higher pressure than supplied pressure is required, the pressure intensifying cylinder 17 applies the same pressure to the plural pistons 19a, 19b so as to obtain compressed fluid of higher pressure due to its boosting effect. Since no air tank is needed, the apparatus is small in size. It does not need useless energy or it is energy-saving because it operates only when high pressure is required.