A vehicular opening/closing body control device includes a braking controller configured to apply a braking force to an opening/closing body, a full-closing detection unit configured to detect that the opening/closing body is in a fully-closed state, and a failure detection unit configured to detect failure of a latch mechanism provided on the opening/closing body. The latch mechanism is provided with a pawl switch, which is switched between ON and OFF states in conjunction with operation of a pawl. The failure detection unit detects, based on the ON and OFF states of the pawl switch, occurrence of an engagement failure in which the latch mechanism fails to hold the opening/closing body in the fully-closed state. The braking controller executes braking control for applying the braking force to the opening/closing body when the engagement failure is detected in the latch.