A microneedle patch application device for inserting a microneedle array into a skin, by pressing a microneedle patch provided with the microneedle array on a first surface of a patch body, from a second surface opposite to the first surface, wherein the microneedle patch application comprises: a casing body having, at one end, an opening through which the microneedle patch passes; a pressing member having a tip surface for pressing the second surface of the microneedle patch, the pressing member being disposed movably in a first direction, in which the microneedle array is moved outward through the opening, and a second direction opposite to the first direction in the casing body; a first biasing means provided in the casing body and disposed to bias the pressing member in the first direction; and a locking member connected to the casing body, the pressing member is provided with a locking part which is engaged with the locking member so as to regulate movement of the pressing member in the first direction, the microneedle patch application device further comprises a lock-releasing member having a protruding part disposed outside the opening of the casing body and protruding from a peripheral part of the opening of the casing body in the first direction, the lock-releasing member being movable in the second direction and being provided associated with the locking member so as to release a locked state in which the locking member is locked on the locking part when the protruding part moves in the second direction, a window part for inserting the microneedle patch is formed on a surface different from the surface provided with the opening of the casing body, and in order that a set state in which the tip surface of the pressing member is drawn from the opening along the second direction and faces the window part for inserting the microneedle patch and an application state in which the tip surface of the pressing member protrudes outside the opening of the casing body in the first direction can be taken, the locking member is in the locked state in the set state, and when the locked state is released with the lock-releasing member, the tip surface of the pressing member is moved by biasing force of the first biasing means to bring into the application state. a casing body having, at one end, an opening through which the microneedle patch passes; a pressing member having a tip surface for pressing the second surface of the microneedle patch, the pressing member being disposed movably in a first direction, in which the microneedle array is moved outward through the opening, and a second direction opposite to the first direction in the casing body; a first biasing means provided in the casing body and disposed to bias the pressing member in the first direction; and a locking member connected to the casing body, the pressing member is provided with a locking part which is engaged with the locking member so as to regulate movement of the pressing member in the first direction, the microneedle patch application device further comprises a lock-releasing member having a protruding part disposed outside the opening of the casing body and protruding from a peripheral part of the opening of the casing body in the first direction, the lock-releasing member being movable in the second direction and being provided associated with the locking member so as to release a locked state in which the locking member is locked on the locking part when the protruding part moves in the second direction, a window part for inserting the microneedle patch is formed on a surface different from the surface provided with the opening of the casing body, and in order that a set state in which the tip surface of the pressing member is drawn from the opening along the second direction and faces the window part for inserting the microneedle patch and an application state in which the tip surface of the pressing member protrudes outside the opening of the casing body in the first direction can be taken, the locking member is in the locked state in the set state, and when the locked state is released with the lock-releasing member, the tip surface of the pressing member is moved by biasing force of the first biasing means to bring into the application state.