Engine

An engine comprising:

• a cylinder chamber, an intake valve, an exhaust valve, and a spark plug,
• wherein inside the cylinder chamber, opposing pistons are arranged so as to reciprocate, an extension space, which is a space extending from a side surface of the cylinder chamber along a direction orthogonal to a central axis of the cylinder chamber, is formed, on a first side surface of the extension space,
• the intake valve is arranged, on a second side surface of the extension space, which opposes the first side surface, the exhaust valve and the spark plug are arranged, and inside the extension space, an electrode formed at a tip of the spark plug is closer to the central axis of the cylinder chamber than an extension line of a central axis of the intake valve and an extension line of a central axis of the exhaust valve.