A dental syringe in which dental material is to be injected into a syringe body from a discharge port, the dental syringe comprising: the syringe body including the discharge port arranged at a front end and a plunger insertion port arranged at a rear end; a plunger to be inserted into the syringe body from the plunger insertion port; and an 0-ring to be mounted in an engagement groove formed along a circumferential direction of a front end portion of the plunger, the 0-ring being held in contact with an outer face of the engagement groove and an inner face of the syringe body; wherein the engagement groove of the plunger includes a shallow groove arranged at a front end side and a deep groove arranged at a rear end side; wherein the shallow groove is arranged such that when the dental material starts being injected into the syringe body from the discharge port and the plunger is moved toward the rear end side, the O-ring stops the plunger from moving within the syringe body, and after air is discharged toward the rear end side of the syringe body from a gap formed between the 0-ring and the syringe body and/or a gap formed between the 0-ring and the plunger, the 0-ring is held in contact with the inner face of the syringe body with a strength that allows the plunger to be pushed and moved along with the 0-ring toward the rear end side by the dental material injected from the discharge port of the syringe body; and wherein when an end portion at the rear end side of the plunger is pushed by a finger to discharge the dental material injected into the syringe body from the discharge port of the syringe body, the O-ring is moved from the shallow groove to the deep groove. the syringe body including the discharge port arranged at a front end and a plunger insertion port arranged at a rear end; a plunger to be inserted into the syringe body from the plunger insertion port; and an 0-ring to be mounted in an engagement groove formed along a circumferential direction of a front end portion of the plunger, the 0-ring being held in contact with an outer face of the engagement groove and an inner face of the syringe body; wherein the engagement groove of the plunger includes a shallow groove arranged at a front end side and a deep groove arranged at a rear end side; wherein the shallow groove is arranged such that when the dental material starts being injected into the syringe body from the discharge port and the plunger is moved toward the rear end side, the O-ring stops the plunger from moving within the syringe body, and after air is discharged toward the rear end side of the syringe body from a gap formed between the 0-ring and the syringe body and/or a gap formed between the 0-ring and the plunger, the 0-ring is held in contact with the inner face of the syringe body with a strength that allows the plunger to be pushed and moved along with the 0-ring toward the rear end side by the dental material injected from the discharge port of the syringe body; and wherein when an end portion at the rear end side of the plunger is pushed by a finger to discharge the dental material injected into the syringe body from the discharge port of the syringe body, the O-ring is moved from the shallow groove to the deep groove.