To stabilize a quality, easily and conveniently use it, and make maintenance accurate and easy by making common use of double-barrel air tanks by putting them in line symmetry or point symmetry, installing sockets of a block and a unit of an instrumental apparatus and the like for common use, and standardizing and using it.

In a portable compressor 1', a driving motor 2, a low pressure cylinder 3 and a high pressure cylinder 3' are arranged together with a cooling fan 13 on a baseplate 9' installed through an installing screw hole on a pair of double-barrel air tanks 8' and 8'. When the baseplate 9' is installed on a pair of double-barrel air tanks 8' and 8', it is formed so that a position of an installing hole screw is installed in a position capable of making common use of the left and right air tanks by developing in line symmetry or point symmetry by 180°. An air regulator 4 such as an air conditioning apparatus and an instrumental apparatus and the like such a gauge 5 and a coupler 6 are set on the installing screw by sockets 11' as an assembly block.