A cam-switching device that selectively switches between a first cam (15, 25) and a second cam (16, 26) to make valve characteristics of an intake or exhaust valve of an engine variable, the first cam (15, 25) and the second cam (16, 26) being provided corresponding to each of the intake or exhaust valve and having different cam profiles, each of the cam profiles being determined such that a first cam angle range where a valve lift amount of the first cam (15, 25) is greater than a valve lift amount of the second cam (16, 26) and a second cam angle range where a valve lift amount of the second cam (16, 26) is greater than a valve lift amount of the first cam (15, 25) are formed, and the cam-switching device comprising: an intake cam shaft comprising an inner intake camshaft and an outer intake camshaft, and an exhaust camshaft comprising an inner exhaust camshaft and an outer exhaust camshaft; each cam shaft configured to rotate in conjunction with a crank shaft of the engine and provided such that the first cam (15, 25) and the second cam (16, 26) are rotatable together; for each camshaft, a cam shaft moving unit configured to slide the outer cam shaft in an axis direction to selectively switch between the first cam (15, 25) and the second cam (16, 26) cylinder resting units configured to stop opening and closing operations of the intake and exhaust valves to make a cylinder restable; and a cam shaft moving control unit configured to control the cylinder resting units to stop the opening and closing operations of the intake and exhaust valve in the same combustion cycle and control the cam shaft moving units to start sliding the outer camshafts in the first cam angle range in a case of switching from the first cam (15, 25) to the second cam (16, 26) and to control the cylinder resting units to stop the opening and closing operations of the intake and exhaust valves in the same combustion cycle and control the cam shaft moving units to start sliding the outer camshafts in the second cam angle range in a case of switching from the second cam (16, 26) to the first cam (15, 25). the first cam (15, 25) and the second cam (16, 26) being provided corresponding to each of the intake or exhaust valve and having different cam profiles, each of the cam profiles being determined such that a first cam angle range where a valve lift amount of the first cam (15, 25) is greater than a valve lift amount of the second cam (16, 26) and a second cam angle range where a valve lift amount of the second cam (16, 26) is greater than a valve lift amount of the first cam (15, 25) are formed, and the cam-switching device comprising: an intake cam shaft comprising an inner intake camshaft and an outer intake camshaft, and an exhaust camshaft comprising an inner exhaust camshaft and an outer exhaust camshaft; each cam shaft configured to rotate in conjunction with a crank shaft of the engine and provided such that the first cam (15, 25) and the second cam (16, 26) are rotatable together; for each camshaft, a cam shaft moving unit configured to slide the outer cam shaft in an axis direction to selectively switch between the first cam (15, 25) and the second cam (16, 26) cylinder resting units configured to stop opening and closing operations of the intake and exhaust valves to make a cylinder restable; and a cam shaft moving control unit configured to control the cylinder resting units to stop the opening and closing operations of the intake and exhaust valve in the same combustion cycle and control the cam shaft moving units to start sliding the outer camshafts in the first cam angle range in a case of switching from the first cam (15, 25) to the second cam (16, 26) and to control the cylinder resting units to stop the opening and closing operations of the intake and exhaust valves in the same combustion cycle and control the cam shaft moving units to start sliding the outer camshafts in the second cam angle range in a case of switching from the second cam (16, 26) to the first cam (15, 25). an intake cam shaft comprising an inner intake camshaft and an outer intake camshaft, and an exhaust camshaft comprising an inner exhaust camshaft and an outer exhaust camshaft; each cam shaft configured to rotate in conjunction with a crank shaft of the engine and provided such that the first cam (15, 25) and the second cam (16, 26) are rotatable together; for each camshaft, a cam shaft moving unit configured to slide the outer cam shaft in an axis direction to selectively switch between the first cam (15, 25) and the second cam (16, 26) cylinder resting units configured to stop opening and closing operations of the intake and exhaust valves to make a cylinder restable; and a cam shaft moving control unit configured to control the cylinder resting units to stop the opening and closing operations of the intake and exhaust valve in the same combustion cycle and control the cam shaft moving units to start sliding the outer camshafts in the first cam angle range in a case of switching from the first cam (15, 25) to the second cam (16, 26) and to control the cylinder resting units to stop the opening and closing operations of the intake and exhaust valves in the same combustion cycle and control the cam shaft moving units to start sliding the outer camshafts in the second cam angle range in a case of switching from the second cam (16, 26) to the first cam (15, 25).