A lock structure comprising: an engaged body; and an engaging body capable of inserting and removing the engaged body along insertion and removal directions opposite to each other, and capable of locking the inserted engaged body in the insertion direction and the removal direction, respectively, wherein the engaged body includes first and second engaged walls (13, 14) disposed opposite to each other at an interval in an orthogonal direction to the insertion and removal directions, third and fourth engaged walls (15, 16) disposed opposite to each other at an interval in an orthogonal direction to the insertion and removal directions and an opposite arrangement direction of the first and second engaged walls (13, 14), a drainage space surrounded by respective inner wall surfaces of the first to fourth engaged walls (13 to 16), characterized in that an engaged protrusion protruding from an outer wall surface of the second engaged wall, a first communication port through which the drainage space communicates with the outside on the insertion direction side of the engaged protrusion, and a second communication port through which the drainage space communicates with the outside on the removal direction side of the first communication port, and the engaging body includes first and second engaging walls (23, 24) disposed opposite to each other at an interval in the opposite arrangement direction, third and fourth engaging walls (25, 26) disposed opposite to each other at an interval in the orthogonal direction to the insertion and removal directions and the opposite arrangement direction, an accommodation space that is an internal space surrounded by respective inner wall surfaces of the first to fourth engaging walls (23 to 26) and in which the engaged body is accommodated, an insertion port through which the engaged body is inserted into the accommodation space from a tip (11a 1) of an end portion on the insertion direction side, a locking hole that is a penetration hole provided in the second engaging wall and into which the engaged protrusion is inserted when the engaged body is accommodated in the accommodation space, and a communication port through which the accommodation space communicates with the outside on the insertion direction side of the locking hole. an engaged body; and an engaging body capable of inserting and removing the engaged body along insertion and removal directions opposite to each other, and capable of locking the inserted engaged body in the insertion direction and the removal direction, respectively, wherein the engaged body includes first and second engaged walls (13, 14) disposed opposite to each other at an interval in an orthogonal direction to the insertion and removal directions, third and fourth engaged walls (15, 16) disposed opposite to each other at an interval in an orthogonal direction to the insertion and removal directions and an opposite arrangement direction of the first and second engaged walls (13, 14), a drainage space surrounded by respective inner wall surfaces of the first to fourth engaged walls (13 to 16), characterized in that an engaged protrusion protruding from an outer wall surface of the second engaged wall, a first communication port through which the drainage space communicates with the outside on the insertion direction side of the engaged protrusion, and a second communication port through which the drainage space communicates with the outside on the removal direction side of the first communication port, and the engaging body includes first and second engaging walls (23, 24) disposed opposite to each other at an interval in the opposite arrangement direction, third and fourth engaging walls (25, 26) disposed opposite to each other at an interval in the orthogonal direction to the insertion and removal directions and the opposite arrangement direction, an accommodation space that is an internal space surrounded by respective inner wall surfaces of the first to fourth engaging walls (23 to 26) and in which the engaged body is accommodated, an insertion port through which the engaged body is inserted into the accommodation space from a tip (11a 1) of an end portion on the insertion direction side, a locking hole that is a penetration hole provided in the second engaging wall and into which the engaged protrusion is inserted when the engaged body is accommodated in the accommodation space, and a communication port through which the accommodation space communicates with the outside on the insertion direction side of the locking hole.