A seat sliding device for preventing accidental operation of the operation member. The seat sliding device includes a biasing member 60 which biases a lock member 50 in response to the operation of an operation lever 70 in an unlocking pivoting direction and which is tiltable around a shaft 62 as the tilting center together with the operation lever 70 in response to the operation of the operation lever 70. A balancer 64 of the biasing member 60 has a shape and mass, etc. adapted so as to bring a position of the center of gravity of the tilting body including the operation lever 70 and the biasing member 60 close to the shaft center of the shaft 62.