A locking device comprising: a pair of shells (110, 110') having flanges that are in surface contact with a casing and a cover, any one of the shells (110, 110') being provided with a locking housing through which a catch hole is formed, a remaining one of the shells being provided with a vertical-movement support block to guide a vertical movement of a locking hook by rotation of a handle; a housing secured to the shell (110, 110') having the vertical-movement support block to guide an operation of a tilting guide; the tilting guide resiliently provided in the housing via a wire spring to guide a movement of the locking hook; the locking hook caught by the catch hole of the locking housing to set a locking state or removed from the catch hole to release the set locking state, while the locking hook is moved along the tilting guide by a forward or backward rotation of the handle; the handle rotatably provided on the tilting guide to move the locking hook forwards or rearwards; a vertical moving block protruding from a lower surface of the locking hook, the vertical moving block being guided along the vertical-movement support block to be in line contact therewith, thus moving up the locking hook that is moved forwards when the handle rotates forwards; and a restoring part connected to the tilting guide and the housing to move down the locking hook and the tilting guide that are moved up while the vertical moving block is in line contact with the vertical-movement support block, thus restoring the locking hook and the tilting guide to original positions thereof; characterized in that a corner of the vertical-movement support block is formed to protrude at right angles so that the vertical moving block is in line contact with the vertical-movement support block in a longitudinal direction to be moved up and down; and an elongated guide hole is formed through the locking hook in a straight line to guide a rotary motion of an eccentric pin for connecting the handle to the locking hook. a pair of shells (110, 110') having flanges that are in surface contact with a casing and a cover, any one of the shells (110, 110') being provided with a locking housing through which a catch hole is formed, a remaining one of the shells being provided with a vertical-movement support block to guide a vertical movement of a locking hook by rotation of a handle; a housing secured to the shell (110, 110') having the vertical-movement support block to guide an operation of a tilting guide; the tilting guide resiliently provided in the housing via a wire spring to guide a movement of the locking hook; the locking hook caught by the catch hole of the locking housing to set a locking state or removed from the catch hole to release the set locking state, while the locking hook is moved along the tilting guide by a forward or backward rotation of the handle; the handle rotatably provided on the tilting guide to move the locking hook forwards or rearwards; a vertical moving block protruding from a lower surface of the locking hook, the vertical moving block being guided along the vertical-movement support block to be in line contact therewith, thus moving up the locking hook that is moved forwards when the handle rotates forwards; and a restoring part connected to the tilting guide and the housing to move down the locking hook and the tilting guide that are moved up while the vertical moving block is in line contact with the vertical-movement support block, thus restoring the locking hook and the tilting guide to original positions thereof; characterized in that a corner of the vertical-movement support block is formed to protrude at right angles so that the vertical moving block is in line contact with the vertical-movement support block in a longitudinal direction to be moved up and down; and an elongated guide hole is formed through the locking hook in a straight line to guide a rotary motion of an eccentric pin for connecting the handle to the locking hook.