An engine system comprising: an engine unit that includes an engine and a rotation driver; a friction detector configured to detect a first parameter corresponding to friction of the engine; a pressure detector configured to detect a current flowing in the rotation driver as a second parameter corresponding to pressure in a combustion chamber of the engine; and a controller configured to control the engine unit based on the first parameter detected by the friction detector and the second parameter detected by the pressure detector, wherein the engine includes a fuel injection device arranged to inject fuel into an intake passage for leading air to the combustion chamber, an ignition device configured to ignite a fuel-air mixture in the combustion chamber, and a valve driver configured to respectively drive an intake valve configured to open and close an intake port and an exhaust valve configured to open and close an exhaust port, the rotation driver is configured to drive rotation of a crankshaft in forward and reverse directions, the controller is configured to control the engine unit to perform a reverse rotation start-up operation during start-up of the engine, wherein the fuel-air mixture is introduced into the combustion chamber while the crankshaft is rotated in the reverse direction, and the fuel-air mixture is ignited such that the crankshaft is rotated in the forward direction, in the reverse rotation start-up operation, wherein the controller is configured to set an ignition threshold value based on the first parameter detected by the friction detector such that the larger the friction of the engine is, the larger the ignition threshold value is, and to control the ignition device such that the ignition is performed when the current detected by the pressure detector reaches the set ignition threshold value, in the reverse rotation start-up operation, and a relationship between the first parameter and the ignition threshold value is determined such that a crank angle of when the fuel-air mixture is ignited is constant. an engine unit that includes an engine and a rotation driver; a friction detector configured to detect a first parameter corresponding to friction of the engine; a pressure detector configured to detect a current flowing in the rotation driver as a second parameter corresponding to pressure in a combustion chamber of the engine; and a controller configured to control the engine unit based on the first parameter detected by the friction detector and the second parameter detected by the pressure detector, wherein the engine includes a fuel injection device arranged to inject fuel into an intake passage for leading air to the combustion chamber, an ignition device configured to ignite a fuel-air mixture in the combustion chamber, and a valve driver configured to respectively drive an intake valve configured to open and close an intake port and an exhaust valve configured to open and close an exhaust port, the rotation driver is configured to drive rotation of a crankshaft in forward and reverse directions, the controller is configured to control the engine unit to perform a reverse rotation start-up operation during start-up of the engine, wherein the fuel-air mixture is introduced into the combustion chamber while the crankshaft is rotated in the reverse direction, and the fuel-air mixture is ignited such that the crankshaft is rotated in the forward direction, in the reverse rotation start-up operation, wherein the controller is configured to set an ignition threshold value based on the first parameter detected by the friction detector such that the larger the friction of the engine is, the larger the ignition threshold value is, and to control the ignition device such that the ignition is performed when the current detected by the pressure detector reaches the set ignition threshold value, in the reverse rotation start-up operation, and a relationship between the first parameter and the ignition threshold value is determined such that a crank angle of when the fuel-air mixture is ignited is constant.