PURPOSE: To eliminate the danger of a latch being released inadvertently even if an extension ladder is moved with its upper ladder gripped by enabling the end of a lock lever in an approximately horizontal position to be engaged with a rung of the upper ladder when an operating rope is not pulled.

CONSTITUTION: When an operating rope 17 is pulled, a rope lever 15 is rotated downwards against the force of a spring. Then the end of the lever comes to a position where it is not engaged with any rung 3a of an upper ladder 3, so unobstructing the rise and fall of the upper ladder 3. In that state, when the operating rope 17 is further strongly pulled, the upper ladder 3 is extended to rise. When the rope is released in a desired position, a latch 6 is latched with a rung 2a to hold the upper ladder in that position. In that sate, a lock lever 16 is restored to a horizontal position. To retract and lower the upper ladder 3, the ladder is raised a certain distance by pulling of the rope 17, then an unlocking piece 8 enters an operating state, the ladder 3 is lowered, and a bracket 5 becomes engaged with a stopper 18 when the ladder 3 is in its most retracted position. A safe extension ladder is thus provided.