The purpose of this study is to evaluate pharmacokinetics, efficacy and safety of Z-338 of pediatric patients with functional dyspepsia (FD).

In Part 1, the pharmacokinetics and safety of single oral dose of Z-338 100 mg are evaluated.

In Part 2, the efficacy and safety of Z-338 100 mg orally 3 times daily before meals are evaluated.

Part 2 is comprised by the double-blind phase and the open-label phase. In the double-blind phase, subjects will take Z-338 or placebo for 28 days. In the open-label phase, all subjects will take Z-338 for 28 days.

Main Inclusion Criteria:

Part 1& Part 2

• Subjects aged from nine to 17 years (from nine to 14 years in Part 1), on the day the informed consent is signed.
• Subjects with a diagnosis of FD as defined by the Rome IV Criteria.
• Subjects who have postprandial fullness, upper abdominal bloating or early satiation.

Part 2 only

• Subjects who have postprandial fullness, upper abdominal bloating or early satiation during with a certain severity during a week prior to the day of randomization.

Main Exclusion Criteria:

Part 1&Part 2

• Subject who have organic diseases of the gastrointestinal tract or gastrointestinal bleeding within 24 weeks prior to informed consent.
• Subject who have received Helicobacter pylori eradication therapy within 24 weeks prior to informed consent, or subjects who is defined as Helicobacter pylori-positive within 4 weeks prior to or on the day the informed consent is signed.
• Subjects who have alarm symptom on the day the informed consent is signed.
• Subjects who have food allergy of unknown origin or uncontrolled food allergy.

Part 2 only

• Subject taking drugs used for FD within 2 weeks prior to the day of randomization (excluding proton pump inhibitors)
• Subject taking proton pump inhibitors within 4 weeks prior to the day of randomization.