A seat slide apparatus for a vehicle, comprising: a first rail including a pair of flanges arranged next to each other in a width direction of the vehicle and including ends, at each of which a locked portion is formed; a second rail movably connected relative to the first rail and including a pair of side wall portions arranged next to each other between the flanges in the width direction, the second rail including bearing holes, each axis line of which extends in the width direction; a lock member including a pair of vertical wall portions which are arranged next to each other between the side wall portions in the width direction and at which a shaft portion supported in the bearing holes is arranged, and a lock portion engageable with and disengageable from the locked portion, the lock member rotating around the bearing holes to engage the lock portion with the locked portion and disengage the lock portion from the locked portion to selectively bring a relative movement between the first rail and the second rail into a locked state; a biasing member biasing the lock member to rotate in a direction in which the relative movement between the first rail and the second rail is brought in the locked state; and an operation member configured to transmit an operating force for releasing the locked state of the relative movement to the lock member, characterised in that a fracture opening (18, 71) is formed at each of the side wall portions and is positioned next to each of the bearing holes in a separating manner from the bearing hole in a direction of the relative movement between the first rail and the second rail, the fracture opening (18, 71) allowing the shaft portion to shift from the bearing hole in a case where a load is inputted in the direction of the relative movement, and in that a restriction portion is formed at the second rail and is configured to restrict the lock member from rotating in a direction in which the locked state of the relative movement is released in a case where the shaft portion shifts from the bearing hole. a first rail including a pair of flanges arranged next to each other in a width direction of the vehicle and including ends, at each of which a locked portion is formed; a second rail movably connected relative to the first rail and including a pair of side wall portions arranged next to each other between the flanges in the width direction, the second rail including bearing holes, each axis line of which extends in the width direction; a lock member including a pair of vertical wall portions which are arranged next to each other between the side wall portions in the width direction and at which a shaft portion supported in the bearing holes is arranged, and a lock portion engageable with and disengageable from the locked portion, the lock member rotating around the bearing holes to engage the lock portion with the locked portion and disengage the lock portion from the locked portion to selectively bring a relative movement between the first rail and the second rail into a locked state; a biasing member biasing the lock member to rotate in a direction in which the relative movement between the first rail and the second rail is brought in the locked state; and an operation member configured to transmit an operating force for releasing the locked state of the relative movement to the lock member, characterised in that a fracture opening (18, 71) is formed at each of the side wall portions and is positioned next to each of the bearing holes in a separating manner from the bearing hole in a direction of the relative movement between the first rail and the second rail, the fracture opening (18, 71) allowing the shaft portion to shift from the bearing hole in a case where a load is inputted in the direction of the relative movement, and in that a restriction portion is formed at the second rail and is configured to restrict the lock member from rotating in a direction in which the locked state of the relative movement is released in a case where the shaft portion shifts from the bearing hole.