An adjusting device includes a connecting member having a chamber. The connecting member further includes first and second openings defined in two ends thereof and communicated with the chamber. The connecting member further includes a first assembling portion in the chamber and a threaded portion in the second opening. A through-hole extends from an inner periphery through an outer periphery of the connecting member and communicates with the chamber. An adjusting member includes a pivotal end having a second assembling portion for assembling with the first assembling portion. The adjusting member further includes a passage having first and second openings respectively in two ends thereof. The first opening of the adjusting member is located in the pivotal end. A sealing cap is in threading connection with the threaded portion. A damper and a damp adjustment cylinder can be coupled to the adjusting device to form a vehicular shock absorber.