Syringe with safety mechanism

A syringe with safety mechanism comprising:

• a syringe;
• a needle connected to a tip end portion of the syringe;
• a holder fixed to the syringe;
• and
• a needle cover displaceable relatively with respect to the syringe along an axial direction of the syringe from a use position where the needle is exposed toward a protection position where the needle is surrounded, wherein
• the holder includes a locking portion that locks the needle cover at the use position from a radially inner side of the needle cover to hold the needle cover at the use position and locks the needle cover at the protection position from the radially inner side to hold the needle cover at the protection position,
• the needle cover includes an expansion portion that expands toward the holder,
• the holder includes a receiving portion that is opposed in the axial direction to the expansion portion of the needle cover at the protection position and abuts on the expansion portion when the needle cover is displaced from the protection position toward the use position along the axial direction to thereby restrict relative displacement of the needle cover with respect to the syringe along the axial direction of the syringe from the protection position toward the use position,
• the holder includes a guide protrusion in a shape protruding toward the needle cover,
• the needle cover is provided with a guide groove that guides the guide protrusion when the needle cover is displaced from the use position toward the protection position,
• the guide groove includes a guide surface in a shape that causes the needle cover to rotate around a central axis of the syringe when the needle cover is displaced from the use position to the protection position,
• the holder includes
• a first wall portion formed at a position where the first wall portion is opposed to the expansion portion of the needle cover at the use position in a radial direction of the needle cover, the first wall portion allowing displacement of the needle cover from the use position toward the protection position while the needle cover rotates around the central axis of the syringe, and
• a second wall portion provided at a position adjacent to the first wall portion in a direction identical to a direction of rotation of the needle cover around the central axis of the syringe when the needle cover is displaced from the use position to the protection position, and
• a tip end portion of the second wall portion in an orientation in which the needle cover moves from the use position toward the protection position constitutes the receiving portion.