A valve timing controller comprising: a driving-side rotary member rotated in synchronism with a crankshaft of an internal combustion engine; a driven-side rotary member mounted on a same shaft as the driving-side rotary member and rotated in synchronism with a valve opening/closing cam shaft of the internal combustion engine; a fluid pressure chamber formed by the driving-side rotary member and the driven-side rotary member; an advancing chamber (Ca) and a retarding chamber (Cb) formed as the fluid pressure chamber is partitioned by a partitioning portion provided in at least one of the driving-side rotary member and the driven-side rotary member; an intermediate locking mechanism including a locking member accommodated in at least one rotary member of the driving-side rotary member and the driven-side rotary member and projectable/retractable to/from the other rotary member of the driving-side rotary member and the driven-side rotary member, and a recess portion formed in the other rotary member to be engageable with the locking member when this locking member projects, the intermediate locking mechanism being switchable between a locking state wherein a relative rotational phase of the driven-side rotary member relative to the driving-side rotary member is restrained to an intermediate locking phase between a most retarded phase and a most advanced phase and a lock-releasing state wherein the restraint is released as the locking member retracts from the recess portion; and a controlling section for controlling supplying or discharging of the work fluid to or from the advancing chamber (Ca) and supplying or discharging of the work fluid to or from the retarding chamber (Cb), characterized in that when the controlling section outputs a phase maintenance signal indicating a phase maintaining state which allows control for maintaining the relative rotational phase within a predetermined angle range by the work fluid present in the advancing chamber (Ca) and the retarding chamber (Cb) under the locking state, based on the phase maintenance signal and with lapse of a predetermined period, the controlling section confirms that the advancing chamber (Ca) and the retarding chamber (Cb) have been filled with the work fluid and effects control to stop the supplying and the discharging of the work fluid to or from the retarding chamber (Cb) and the advancing chamber (Ca) with the relative rotational phase being the intermediate locking phase and instructs switchover from the locking state to the lock-releasing state, whereby the intermediate locking mechanism is switched over to the lock-releasing state and the relative rotational phase is maintained to the intermediate locking phase. a driving-side rotary member rotated in synchronism with a crankshaft of an internal combustion engine; a driven-side rotary member mounted on a same shaft as the driving-side rotary member and rotated in synchronism with a valve opening/closing cam shaft of the internal combustion engine; a fluid pressure chamber formed by the driving-side rotary member and the driven-side rotary member; an advancing chamber (Ca) and a retarding chamber (Cb) formed as the fluid pressure chamber is partitioned by a partitioning portion provided in at least one of the driving-side rotary member and the driven-side rotary member; an intermediate locking mechanism including a locking member accommodated in at least one rotary member of the driving-side rotary member and the driven-side rotary member and projectable/retractable to/from the other rotary member of the driving-side rotary member and the driven-side rotary member, and a recess portion formed in the other rotary member to be engageable with the locking member when this locking member projects, the intermediate locking mechanism being switchable between a locking state wherein a relative rotational phase of the driven-side rotary member relative to the driving-side rotary member is restrained to an intermediate locking phase between a most retarded phase and a most advanced phase and a lock-releasing state wherein the restraint is released as the locking member retracts from the recess portion; and a controlling section for controlling supplying or discharging of the work fluid to or from the advancing chamber (Ca) and supplying or discharging of the work fluid to or from the retarding chamber (Cb), characterized in that when the controlling section outputs a phase maintenance signal indicating a phase maintaining state which allows control for maintaining the relative rotational phase within a predetermined angle range by the work fluid present in the advancing chamber (Ca) and the retarding chamber (Cb) under the locking state, based on the phase maintenance signal and with lapse of a predetermined period, the controlling section confirms that the advancing chamber (Ca) and the retarding chamber (Cb) have been filled with the work fluid and effects control to stop the supplying and the discharging of the work fluid to or from the retarding chamber (Cb) and the advancing chamber (Ca) with the relative rotational phase being the intermediate locking phase and instructs switchover from the locking state to the lock-releasing state, whereby the intermediate locking mechanism is switched over to the lock-releasing state and the relative rotational phase is maintained to the intermediate locking phase.