Provided is an unconstrained wearable spirometer apparatus. The apparatus includes a variable resistor including a conductive yarn, the length of which changes according to a change in circumference of ones chest when breathing, and having a resistance which changes according to a change in length of the conductive yarn, a resistance-voltage converter converting the resistance of the variable resistor into a voltage, an analog-digital converter converting the voltage in an analog-digital manner, and digitizing the converted results, a cross-sectional capacity calculator calculating changes in cross-sectional capacity of ones chest according to the digitized voltage, an adder adding the calculated changes in cross-sectional capacity and calculating lung capacity, and a transmitter externally transmitting the calculated lung capacity information. Therefore, lung capacity can be measured by wearing such an apparatus in the form of clothing without the use of an external apparatus or device.
