A valve timing adjusting device includes a housing, a vane rotor, a sleeve, and a spool. The housing includes a timing pulley connected to a crank shaft through a dry belt, and rotates in association with the crank shaft. The sleeve includes a supply port, a drain port, a first control port, a second control port, and a first drain oil channel. The spool includes an oil connection channel that is arranged at an axial center portion of the spool and controls the supply port to be connected with the first control port or the second control port depending on an axial-direction position. The drain port is connected with a first drain space through a second drain oil channel. A second drain space is connected with the first drain space through a third drain oil channel that is provided to span the vane rotor and the cam shaft.