This invention provides a multi-layer diaphragm which is for use in fluid devices and has excellent maintainability in addition to both operability and pressure resistance. This multi-layer diaphragm is provided with a first and second plate and with an elastic adhesive layer which binds together the first and second metal plates. The elastic adhesive layer has an elastic layer that is elastic in a direction which offsets the first and second metal plates from one another in the in-plane direction. The multi-layer diaphragm is provided with a metal mounting plate which, provided in a position allowing protrusion beyond the first and second metal plates in the outer edge direction, has a mounting unit for mounting to the fluid device.