A mask apparatus comprising: a mask body having an inlet and an outlet, the mask body including: a rear body; and a front body coupled to a front surface of the rear body; a face guard that is coupled to a rear surface of the rear body, that is configured to accommodate a portion of user's face, and that defines a respiration space at an inner side thereof; and an air cleaning module that is mounted on the rear body, that is configured to purify air introduced into the inlet, and that is configured to supply the purified air to the respiration space, wherein a portion of the rear body protrudes toward the front body to define a accommodation portion to accommodate the air cleaning module, wherein the accommodation portion includes: a fastening surface extending forward from a side end portion of the rear body, a seating surface that extends toward a center of the rear body from an end portion of the fastening surface and that accommodates the air cleaning module, and an air guide surface connecting an end portion of the seating surface to a front surface of the rear body, wherein the air cleaning module includes: a fan module disposed at a seating surface of the accommodation portion, a filter that is disposed at a rear side of the fan module and that is configured to purify air flowing into the fan module, and a filter housing including a filter frame that surrounds a side surface of the filter and a filter cover that covers a rear surface of the filter, and wherein the inlet is provided at the filter cover in a rear surface of the rear body and disposed at an outside of the face guard, to introduce ambient air into the mask body through the inlet, and wherein the outlet is provided in the rear surface of the rear body and disposed at an inside of the face guard, to supply the purified air into the respiration space through the outlet. a mask body having an inlet and an outlet, the mask body including: a rear body; and a front body coupled to a front surface of the rear body; a rear body; and a front body coupled to a front surface of the rear body; a face guard that is coupled to a rear surface of the rear body, that is configured to accommodate a portion of user's face, and that defines a respiration space at an inner side thereof; and an air cleaning module that is mounted on the rear body, that is configured to purify air introduced into the inlet, and that is configured to supply the purified air to the respiration space, wherein a portion of the rear body protrudes toward the front body to define a accommodation portion to accommodate the air cleaning module, wherein the accommodation portion includes: a fastening surface extending forward from a side end portion of the rear body, a seating surface that extends toward a center of the rear body from an end portion of the fastening surface and that accommodates the air cleaning module, and an air guide surface connecting an end portion of the seating surface to a front surface of the rear body, wherein the air cleaning module includes: a fan module disposed at a seating surface of the accommodation portion, a filter that is disposed at a rear side of the fan module and that is configured to purify air flowing into the fan module, and a filter housing including a filter frame that surrounds a side surface of the filter and a filter cover that covers a rear surface of the filter, and wherein the inlet is provided at the filter cover in a rear surface of the rear body and disposed at an outside of the face guard, to introduce ambient air into the mask body through the inlet, and wherein the outlet is provided in the rear surface of the rear body and disposed at an inside of the face guard, to supply the purified air into the respiration space through the outlet. a fastening surface extending forward from a side end portion of the rear body, a seating surface that extends toward a center of the rear body from an end portion of the fastening surface and that accommodates the air cleaning module, and an air guide surface connecting an end portion of the seating surface to a front surface of the rear body, wherein the air cleaning module includes: a fan module disposed at a seating surface of the accommodation portion, a filter that is disposed at a rear side of the fan module and that is configured to purify air flowing into the fan module, and a filter housing including a filter frame that surrounds a side surface of the filter and a filter cover that covers a rear surface of the filter, and wherein the inlet is provided at the filter cover in a rear surface of the rear body and disposed at an outside of the face guard, to introduce ambient air into the mask body through the inlet, and wherein the outlet is provided in the rear surface of the rear body and disposed at an inside of the face guard, to supply the purified air into the respiration space through the outlet. a fan module disposed at a seating surface of the accommodation portion, a filter that is disposed at a rear side of the fan module and that is configured to purify air flowing into the fan module, and a filter housing including a filter frame that surrounds a side surface of the filter and a filter cover that covers a rear surface of the filter, and wherein the inlet is provided at the filter cover in a rear surface of the rear body and disposed at an outside of the face guard, to introduce ambient air into the mask body through the inlet, and wherein the outlet is provided in the rear surface of the rear body and disposed at an inside of the face guard, to supply the purified air into the respiration space through the outlet.