A door latch device is provided which has a childproof locking mechanism of which a childproof lever is pivotally supported by a support shaft. The childproof lever of the childproof locking mechanism is pivotally supported on a casing by the support shaft extending in a transverse direction of a vehicle. This mechanism shifting between a childproof unlock state, in which a door opening operation by an inside handle is transmitted to an engagement mechanism, and a childproof lock state, in which this opening operation is not transmitted, and a manual operation part is formed at an end portion of the childproof lever in a longitudinal direction of a vehicle perpendicular to the support shaft such that this manual operation part passes through a cover member and projects backward.