To provide a clamp and an engaging structure providing better controllability for disengagement than conventional products.

When the engaging member 21 and the member 23 to be engaged of the clamp 1 are brought into engagement with each other, the engaging member 21 is advanced (lowered) to an engagement position while a guided projection 35 is being guided to the inside (right side) of a guide part 51, so that an engagement pawl 33 is caught by a stepped part 43 to bring the engaging member 21 into engagement with the member 23 to be engaged. To move them out of engagement, the engaging member 21 is further advanced (lowered) to cause the end of the engaging member 21 to slide along a first inclined face 53 and cause the guided projection 35 to escape outside of the guide part 51 upon movement beyond the edge of the guide part,51. Thereafter, the engaging member 21 is moved backward (raised) to guide the guided projection 35 on the outside of the guide part 51 and allow the engagement pawl 33 to pass through the engagement position without being caught by the stepped part 43.