A compressor apparatus comprising: a motor; a rotational shaft rotary-driven by the motor; a compressor main body comprising a rod attached to the rotational shaft via a crank, a piston disposed in the rod end, and a cylinder housing reciprocatingly the piston and forming a cylinder chamber for compressing the air between said piston and the cylinder; and an air-supplying means having an air-supplying flow channel to supply the compressed-air from said cylinder chamber into a tire; a detection means which notifies a user that a pressure of the compressed-air supplied from said cylinder chamber exceeds a reference pressure and prompts the user to turn off said motor; and a storage case in which the motor, the rotational shaft, the compressor main body, the air-supplying means and the detection means are arranged, wherein said detection means includes a valve main body having a valve flow channel including one end leading to the air-supplying flow channel and another end leading to an exhaust port, a switch valve intermediating in the valve flow channel and releasing the valve flow channel to exhaust the air from said exhaust port when the compressed-air pressure exceeds said reference pressure, characterized in that the detection means further includes a detection cap disposed in said exhaust port and pushed up from a normal position, which is at the same level as an outer surface of said storage case or on the inward side of the outer surface, to a protruding position, which protrudes over the outer surface of said storage case, by the air pressure exhausted from said exhaust port, and a retaining means to keep said detection cap at said normal position when said compressed-air is below the reference pressure. a motor; a rotational shaft rotary-driven by the motor; a compressor main body comprising a rod attached to the rotational shaft via a crank, a piston disposed in the rod end, and a cylinder housing reciprocatingly the piston and forming a cylinder chamber for compressing the air between said piston and the cylinder; and a rod attached to the rotational shaft via a crank, a piston disposed in the rod end, and a cylinder housing reciprocatingly the piston and forming a cylinder chamber for compressing the air between said piston and the cylinder; and an air-supplying means having an air-supplying flow channel to supply the compressed-air from said cylinder chamber into a tire; a detection means which notifies a user that a pressure of the compressed-air supplied from said cylinder chamber exceeds a reference pressure and prompts the user to turn off said motor; and a storage case in which the motor, the rotational shaft, the compressor main body, the air-supplying means and the detection means are arranged, a valve main body having a valve flow channel including one end leading to the air-supplying flow channel and another end leading to an exhaust port, a switch valve intermediating in the valve flow channel and releasing the valve flow channel to exhaust the air from said exhaust port when the compressed-air pressure exceeds said reference pressure, a valve flow channel including one end leading to the air-supplying flow channel and another end leading to an exhaust port, a switch valve intermediating in the valve flow channel and releasing the valve flow channel to exhaust the air from said exhaust port when the compressed-air pressure exceeds said reference pressure, characterized in that the detection means further includes a detection cap disposed in said exhaust port and pushed up from a normal position, which is at the same level as an outer surface of said storage case or on the inward side of the outer surface, to a protruding position, which protrudes over the outer surface of said storage case, by the air pressure exhausted from said exhaust port, and a retaining means to keep said detection cap at said normal position when said compressed-air is below the reference pressure.