This letter describes the development of a humanoid arm with quick-and-wide motion capability for making humans laugh. Laughter is attracting research attention because it enhances health by treating or preventing mental diseases. However, laughter has not been used effectively in healthcare because the mechanism of laughter is complicated and is yet to be fully understood. The development of a robot capable of making humans laugh will clarify the mechanism how humans experience humor from stimuli. Nonverbal funny expressions have the potential to make humans laugh across cultural and linguistic differences. In particular, we focused on the exaggerated arm motion widely used in slapsticks and silent comedy films. In order to develop a humanoid robot that can perform this type of movement, the required specification was calculated from slapstick skits performed by human comedians. To meet the required specifications, new arms for the humanoid robot were developed with a novel mechanism that includes lightweight joints driven by a flexible shaft and joints with high output power driven by a twin-motor mechanism. The results of experimental evaluation show that the quick-and-wide motion performed by the developed hardware is effective at making humans laugh.