Provided is a mask fitting level determination device that has a significantly simple component configuration, that can be driven by a battery, that can be reduced in size to a palm size, that is inexpensive, that is operated by a simple operation method, and that does not require proficiency for accurate measurement. The mask fitting level determination device includes: a mask inner pressure detection unit 2 that is inserted between a face surface F of a mask wearing person and a worn mask 1； and a circuit control unit that sets a predefined threshold value in accordance with strength of breathing of the mask wearing person and determines a fitting level on the basis of a reference pressure value and a mask inner pressure value measure by the mask inner pressure detection unit 2； and a display unit 3 that displays the fitting level determined by the circuit control unit to the mask wearing person.
