A solenoid includes a plunger, a core, an electromagnetic coil, and a casing. A core receiving portion of the plunger is to receive a core projection while the electromagnetic coil is energized. A plunger receiving portion of the core is to receive a plunger projection while the electromagnetic coil is energized. The casing houses the plunger, the core, and the electromagnetic coil. At least one of an end portion of the plunger projection and an end portion of the core projection has an acute angle in a cross section along the axial direction. A distance between the end portion of the plunger projection and the end portion of the core projection is shortest among distances between the core and the plunger while the electromagnetic coil is not energized.