Seat belt lock device of a child car seat, and a child car seat

A seat belt lock device 21 includes: a main body case 23 having a seat belt insertion hole 22; a belt retaining member 24 that is supported by the main body case 23; a belt lock member 25 that restricts movement of a seat belt; a biasing unit that biases the belt lock member 25; an operation portion 26 that, when shifted from a first position to a second position, presses the belt lock member 25 toward a belt unlock/release position where the seat belt is unlocked or released; and a coupling portion that couples the operation portion 26 and the belt retaining member 24 so that they can operate together.