A seat lock apparatus, comprising: a hook member configured to be rotationally biased elastically in a positive direction; an interlocking means configured to restrict rotation of the hook member in a negative direction; and a cover member configured to cover an operation range of the hook member at one side of the hook member, the cover member including a striker entrance groove (204a, 204b) that a striker enters, wherein the hook member includes: a support shaft provided near one end of the hook member; an inclined hook edge face provided at another end of the hook member, and configured to be rotationally biased in the negative direction by the entering striker coming into contact with the inclined hook edge face; and an engagement groove that has a depth enabling the hook member to be in a locked position by the entering striker fitting into the depth after overriding the inclined hook edge face, the interlocking means is configured to be switched over: to a restricting position of restricting the rotation of the hook member in the negative direction when the hook member is in engagement with the striker and is in the locked position; and to an allowing position of allowing the rotation of the hook member in the negative direction when the striker enters and when an engagement releasing operation for the striker has been performed, and characterized in that the engagement groove has both end portions at a side of an opening of the engagement groove, each end portion being beyond the striker entrance groove (204a, 204b) to overlap the cover member as viewed along a shaft direction of the hook member when the hook member is at a position of being restricted from operating by the interlocking means. a hook member configured to be rotationally biased elastically in a positive direction; an interlocking means configured to restrict rotation of the hook member in a negative direction; and a cover member configured to cover an operation range of the hook member at one side of the hook member, the cover member including a striker entrance groove (204a, 204b) that a striker enters, wherein the hook member includes: a support shaft provided near one end of the hook member; an inclined hook edge face provided at another end of the hook member, and configured to be rotationally biased in the negative direction by the entering striker coming into contact with the inclined hook edge face; and an engagement groove that has a depth enabling the hook member to be in a locked position by the entering striker fitting into the depth after overriding the inclined hook edge face, a support shaft provided near one end of the hook member; an inclined hook edge face provided at another end of the hook member, and configured to be rotationally biased in the negative direction by the entering striker coming into contact with the inclined hook edge face; and an engagement groove that has a depth enabling the hook member to be in a locked position by the entering striker fitting into the depth after overriding the inclined hook edge face, the interlocking means is configured to be switched over: to a restricting position of restricting the rotation of the hook member in the negative direction when the hook member is in engagement with the striker and is in the locked position; and to an allowing position of allowing the rotation of the hook member in the negative direction when the striker enters and when an engagement releasing operation for the striker has been performed, and to a restricting position of restricting the rotation of the hook member in the negative direction when the hook member is in engagement with the striker and is in the locked position; and to an allowing position of allowing the rotation of the hook member in the negative direction when the striker enters and when an engagement releasing operation for the striker has been performed, and characterized in that the engagement groove has both end portions at a side of an opening of the engagement groove, each end portion being beyond the striker entrance groove (204a, 204b) to overlap the cover member as viewed along a shaft direction of the hook member when the hook member is at a position of being restricted from operating by the interlocking means.