1. A wiring device mounting frame holding a wiring device and fixed to a surface of a
structure, the wiring device mounting frame being provided at a front surface thereof with a
wiring device plate detachably, the wiring device plate having an opening that exposes a front
surface of the wiring device, the wiring device mounting frame comprising:
a metallic frame to which the wiring device is attached; and
an engaging member formed of synthetic resin to be separate from the frame, the engaging member being detachably engaged with an engaging part arranged at the wiring device plate,
wherein the engaging member is attached to a mounting hole that goes through the frame, the engaging member comprising:
a body engaged with the engaging part;
a first abutting part projecting from the body, the first abutting part abutting to a periphery of the mounting hole of the frame from one direction of a thickness direction of the frame; and
a second abutting part abutting to a periphery of the mounting hole from the other direction of the thickness direction,
wherein the second abutting part projects in a direction opposite to a direction in which the engaging member is attached to the mounting hole, while the second abutting part is capable of being flexed freely, the second abutting part being mounted at each of both sides of the body.
2. The wiring device mounting frame according to claim 1, wherein the second abutting part is provided so as not to project to a side of a surface of the frame.
3. The wiring device mounting frame according to any one of claim 1 or 2, wherein the body comprises an engaging projection in an insertion hole in which the engaging part is inserted, the engaging projection being engaged with the engaging part.
4. The wiring device mounting frame according to claim 3, wherein the engaging projection is formed into a pillar-shape, the engaging projection having a first peripheral surface and a second peripheral surface, the first peripheral surface facing to a first opening of the mounting hole into which the engaging part is inserted, the first peripheral surface being formed to a curved surface, the second peripheral surface facing to a second opening of the mounting hole which is different from the first opening, the second peripheral surface being formed to a plane surface.
5. The wiring device mounting frame according to claim 3 or 4, wherein the first abutting

part comprises:
a wide-width first abutting part; and
a narrow-width first abutting part having narrower width than the wide-width first abutting part, the narrow-width first abutting part being formed at an outer wall surface of the body of a opposite side to the wide-width first abutting part across the insertion hole.
6. The wiring device mounting frame according to claim 5, wherein the wide-width first
abutting part is adjacent to the engaging projection across a side wall of the body.
7. Awiring apparatus comprising:
a wiring device;
the wiring device mounting frame according to any one of claims 1 to 6, the wiring device mounting frame holding the wiring device and being fixed to a surface of a structure; and
a wiring device plate mounted on a front surface of the wiring device mounting frame detachably.