PROBLEM: To provide a retaining device for which the magnitude of resistance when an engaging protrusion moves between elastic pieces can be adjusted.
SOLUTION: The retaining device 4 is provided with: a receiving member 5 that is attached to a main body 1, and an engagement member 6 that is attached to a movable body 2. The receiving member 5 has: a base part 10 attached to the main body 1, a first elastic piece 11 supported by the base part 10, and a second elastic piece 12 supported by the base part 10. The engagement member 6 has an engaging protrusion 8 that passes between the first elastic piece 11 and the second elastic piece 12 and is retained at a retaining position P. An interval between the first elastic piece 11 and the second elastic piece 12 becomes narrower than the engaging protrusion 8 at a more forward side than the retaining position P. The first elastic piece 11 bends more easily than the second elastic piece 12 at a more forward side than the retaining position P.