A door latch apparatus with a childproof lock mechanism comprising; a housing whose opening surface on a vehicle inner side is covered by a cover; an inside lever operable in an opening direction in accordance with a door opening operation of an inside handle provided in the vehicle inner side, and a childproof lock mechanism that can be switched between a childproof unlocking state where an opening operation of the inside lever can be transmitted and a childproof locking state where the opening operation of the inside lever cannot be transmitted, wherein the childproof lock mechanism comprises, a childproof lever supported by a shaft on the housing and rotatable on the shaft to a childproof unlocking position and a childproof locking position, the childproof lever having a locking projection, a release actuating member which is supported in an elongated guide hole provided in the childproof lever movably from a standby position at a lower end of the elongated guide hole to a release position, a torsion coil spring as a biasing means always biasing the release actuating member toward the standby position, the torsion coil spring having first and second side foot pieces (381,382), wherein the release actuating member has a projecting portion facing a vehicle outer side and a spring receiving projection facing the vehicle inner side, wherein the release actuating member is configured as a separate member from the childproof lever, so that only the release actuating member containing the projecting portion is movable independently in the release direction in conjunction with the opening operation of the inside lever, wherein, when the childproof lever is in the childproof unlocking position, the projecting portion enters to a rotate locus of the inside lever in the opening direction, and when the childproof lever is in the childproof locking position, the projecting portion retreats from the rotate locus of the inside lever, and wherein the release actuating member is configured to be able to move in the elongated guide hole centering on the shaft based on the opening operation of the inside lever, wherein the childproof lever has a shaft hole configured to be fitted to the shaft and spring holding portions provided on the vehicle inner side surrounding the shaft hole for holding the torsion coil spring, wherein the childproof lock mechanism has a subassembly state in which the release actuating member is assembled to the elongated guide hole of the childproof lever, the torsion coil spring is held by the spring holding portions and one side foot piece of the torsion coil spring is locked by the locking projection of the childproof lever and the other side foot piece of the torsion coil spring is contacted against the spring receiving projection of the release actuating member, wherein the release actuating member is configured such that, when the childproof lever is in the childproof unlocking position and when the inside lever is in the opening operation, by the projecting portion configured as the separate member from the childproof lever is brought into abutment with the inside lever and is moved in the opening direction, the release actuating moves to the release position against the biasing power of the biasing means.